diff --git a/src/Makefile.am b/src/Makefile.am
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -106,6 +106,7 @@
   bloom.h \
   blockencodings.h \
   blockfileinfo.h \
+  blockindex.h \
   blockindexworkcomparator.h \
   blockstatus.h \
   blockvalidity.h \
diff --git a/src/chain.h b/src/blockindex.h
copy from src/chain.h
copy to src/blockindex.h
--- a/src/chain.h
+++ b/src/blockindex.h
@@ -1,37 +1,19 @@
-// Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2016 The Bitcoin Core developers
+// Copyright (c) 2018 The Bitcoin developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#ifndef BITCOIN_CHAIN_H
-#define BITCOIN_CHAIN_H
+#ifndef BITCOIN_BLOCKINDEX_H
+#define BITCOIN_BLOCKINDEX_H
 
 #include "arith_uint256.h"
 #include "blockstatus.h"
 #include "blockvalidity.h"
-#include "consensus/params.h"
 #include "diskblockpos.h"
-#include "pow.h"
 #include "primitives/block.h"
 #include "tinyformat.h"
 #include "uint256.h"
 
-#include <unordered_map>
-#include <vector>
-
-/**
- * Maximum amount of time that a block timestamp is allowed to exceed the
- * current network-adjusted time before the block will be accepted.
- */
-static const int64_t MAX_FUTURE_BLOCK_TIME = 2 * 60 * 60;
-
-/**
- * Timestamp window used as a grace period by code that compares external
- * timestamps (such as timestamps passed to RPCs, or wallet key creation times)
- * to block timestamps. This should be set at least as high as
- * MAX_FUTURE_BLOCK_TIME.
- */
-static const int64_t TIMESTAMP_WINDOW = MAX_FUTURE_BLOCK_TIME;
+#include <cstdint>
 
 /**
  * The block chain is a tree shaped structure starting with the genesis block at
@@ -235,176 +217,4 @@
     const CBlockIndex *GetAncestor(int height) const;
 };
 
-/**
- * Maintain a map of CBlockIndex for all known headers.
- */
-struct BlockHasher {
-    size_t operator()(const uint256 &hash) const { return hash.GetCheapHash(); }
-};
-
-typedef std::unordered_map<uint256, CBlockIndex *, BlockHasher> BlockMap;
-extern BlockMap mapBlockIndex;
-
-arith_uint256 GetBlockProof(const CBlockIndex &block);
-
-/**
- * Return the time it would take to redo the work difference between from and
- * to, assuming the current hashrate corresponds to the difficulty at tip, in
- * seconds.
- */
-int64_t GetBlockProofEquivalentTime(const CBlockIndex &to,
-                                    const CBlockIndex &from,
-                                    const CBlockIndex &tip,
-                                    const Consensus::Params &);
-/**
- * Find the forking point between two chain tips.
- */
-const CBlockIndex *LastCommonAncestor(const CBlockIndex *pa,
-                                      const CBlockIndex *pb);
-
-/** Used to marshal pointers into hashes for db storage. */
-class CDiskBlockIndex : public CBlockIndex {
-public:
-    uint256 hashPrev;
-
-    CDiskBlockIndex() { hashPrev = uint256(); }
-
-    explicit CDiskBlockIndex(const CBlockIndex *pindex) : CBlockIndex(*pindex) {
-        hashPrev = (pprev ? pprev->GetBlockHash() : uint256());
-    }
-
-    ADD_SERIALIZE_METHODS;
-
-    template <typename Stream, typename Operation>
-    inline void SerializationOp(Stream &s, Operation ser_action) {
-        int _nVersion = s.GetVersion();
-        if (!(s.GetType() & SER_GETHASH)) {
-            READWRITE(VARINT(_nVersion));
-        }
-
-        READWRITE(VARINT(nHeight));
-        READWRITE(nStatus);
-        READWRITE(VARINT(nTx));
-        if (nStatus.hasData() || nStatus.hasUndo()) {
-            READWRITE(VARINT(nFile));
-        }
-        if (nStatus.hasData()) {
-            READWRITE(VARINT(nDataPos));
-        }
-        if (nStatus.hasUndo()) {
-            READWRITE(VARINT(nUndoPos));
-        }
-
-        // block header
-        READWRITE(this->nVersion);
-        READWRITE(hashPrev);
-        READWRITE(hashMerkleRoot);
-        READWRITE(nTime);
-        READWRITE(nBits);
-        READWRITE(nNonce);
-    }
-
-    uint256 GetBlockHash() const {
-        CBlockHeader block;
-        block.nVersion = nVersion;
-        block.hashPrevBlock = hashPrev;
-        block.hashMerkleRoot = hashMerkleRoot;
-        block.nTime = nTime;
-        block.nBits = nBits;
-        block.nNonce = nNonce;
-        return block.GetHash();
-    }
-
-    std::string ToString() const {
-        std::string str = "CDiskBlockIndex(";
-        str += CBlockIndex::ToString();
-        str += strprintf("\n                hashBlock=%s, hashPrev=%s)",
-                         GetBlockHash().ToString(), hashPrev.ToString());
-        return str;
-    }
-};
-
-/**
- * An in-memory indexed chain of blocks.
- */
-class CChain {
-private:
-    std::vector<CBlockIndex *> vChain;
-
-public:
-    /**
-     * Returns the index entry for the genesis block of this chain, or nullptr
-     * if none.
-     */
-    CBlockIndex *Genesis() const {
-        return vChain.size() > 0 ? vChain[0] : nullptr;
-    }
-
-    /**
-     * Returns the index entry for the tip of this chain, or nullptr if none.
-     */
-    CBlockIndex *Tip() const {
-        return vChain.size() > 0 ? vChain[vChain.size() - 1] : nullptr;
-    }
-
-    /**
-     * Returns the index entry at a particular height in this chain, or nullptr
-     * if no such height exists.
-     */
-    CBlockIndex *operator[](int nHeight) const {
-        if (nHeight < 0 || nHeight >= (int)vChain.size()) {
-            return nullptr;
-        }
-        return vChain[nHeight];
-    }
-
-    /** Compare two chains efficiently. */
-    friend bool operator==(const CChain &a, const CChain &b) {
-        return a.vChain.size() == b.vChain.size() &&
-               a.vChain[a.vChain.size() - 1] == b.vChain[b.vChain.size() - 1];
-    }
-
-    /** Efficiently check whether a block is present in this chain. */
-    bool Contains(const CBlockIndex *pindex) const {
-        return (*this)[pindex->nHeight] == pindex;
-    }
-
-    /**
-     * Find the successor of a block in this chain, or nullptr if the given
-     * index is not found or is the tip.
-     */
-    CBlockIndex *Next(const CBlockIndex *pindex) const {
-        if (!Contains(pindex)) {
-            return nullptr;
-        }
-
-        return (*this)[pindex->nHeight + 1];
-    }
-
-    /**
-     * Return the maximal height in the chain. Is equal to chain.Tip() ?
-     * chain.Tip()->nHeight : -1.
-     */
-    int Height() const { return vChain.size() - 1; }
-
-    /** Set/initialize a chain with a given tip. */
-    void SetTip(CBlockIndex *pindex);
-
-    /**
-     * Return a CBlockLocator that refers to a block in this chain (by default
-     * the tip).
-     */
-    CBlockLocator GetLocator(const CBlockIndex *pindex = nullptr) const;
-
-    /**
-     * Find the last common block between this chain and a block index entry.
-     */
-    const CBlockIndex *FindFork(const CBlockIndex *pindex) const;
-
-    /**
-     * Find the earliest block with timestamp equal or greater than the given.
-     */
-    CBlockIndex *FindEarliestAtLeast(int64_t nTime) const;
-};
-
-#endif // BITCOIN_CHAIN_H
+#endif // BITCOIN_BLOCKINDEX_H
diff --git a/src/blockindexworkcomparator.h b/src/blockindexworkcomparator.h
--- a/src/blockindexworkcomparator.h
+++ b/src/blockindexworkcomparator.h
@@ -5,8 +5,7 @@
 #ifndef BITCOIN_BLOCK_INDEX_WORK_COMPARATOR_H
 #define BITCOIN_BLOCK_INDEX_WORK_COMPARATOR_H
 
-// TODO: Split chain.h apart and only include CBlockIndex
-#include "chain.h"
+#include "blockindex.h"
 
 struct CBlockIndexWorkComparator {
     bool operator()(const CBlockIndex *pa, const CBlockIndex *pb) const {
diff --git a/src/chain.h b/src/chain.h
--- a/src/chain.h
+++ b/src/chain.h
@@ -7,8 +7,7 @@
 #define BITCOIN_CHAIN_H
 
 #include "arith_uint256.h"
-#include "blockstatus.h"
-#include "blockvalidity.h"
+#include "blockindex.h"
 #include "consensus/params.h"
 #include "diskblockpos.h"
 #include "pow.h"
@@ -33,208 +32,6 @@
  */
 static const int64_t TIMESTAMP_WINDOW = MAX_FUTURE_BLOCK_TIME;
 
-/**
- * The block chain is a tree shaped structure starting with the genesis block at
- * the root, with each block potentially having multiple candidates to be the
- * next block. A blockindex may have multiple pprev pointing to it, but at most
- * one of them can be part of the currently active branch.
- */
-class CBlockIndex {
-public:
-    //! pointer to the hash of the block, if any. Memory is owned by this
-    //! CBlockIndex
-    const uint256 *phashBlock;
-
-    //! pointer to the index of the predecessor of this block
-    CBlockIndex *pprev;
-
-    //! pointer to the index of some further predecessor of this block
-    CBlockIndex *pskip;
-
-    //! height of the entry in the chain. The genesis block has height 0
-    int nHeight;
-
-    //! Which # file this block is stored in (blk?????.dat)
-    int nFile;
-
-    //! Byte offset within blk?????.dat where this block's data is stored
-    unsigned int nDataPos;
-
-    //! Byte offset within rev?????.dat where this block's undo data is stored
-    unsigned int nUndoPos;
-
-    //! (memory only) Total amount of work (expected number of hashes) in the
-    //! chain up to and including this block
-    arith_uint256 nChainWork;
-
-    //! Number of transactions in this block.
-    //! Note: in a potential headers-first mode, this number cannot be relied
-    //! upon
-    unsigned int nTx;
-
-    //! (memory only) Number of transactions in the chain up to and including
-    //! this block.
-    //! This value will be non-zero only if and only if transactions for this
-    //! block and all its parents are available. Change to 64-bit type when
-    //! necessary; won't happen before 2030
-    unsigned int nChainTx;
-
-    //! Verification status of this block. See enum BlockStatus
-    BlockStatus nStatus;
-
-    //! block header
-    int32_t nVersion;
-    uint256 hashMerkleRoot;
-    uint32_t nTime;
-    uint32_t nBits;
-    uint32_t nNonce;
-
-    //! (memory only) Sequential id assigned to distinguish order in which
-    //! blocks are received.
-    int32_t nSequenceId;
-
-    //! (memory only) block header metadata
-    uint64_t nTimeReceived;
-
-    //! (memory only) Maximum nTime in the chain upto and including this block.
-    unsigned int nTimeMax;
-
-    void SetNull() {
-        phashBlock = nullptr;
-        pprev = nullptr;
-        pskip = nullptr;
-        nHeight = 0;
-        nFile = 0;
-        nDataPos = 0;
-        nUndoPos = 0;
-        nChainWork = arith_uint256();
-        nTx = 0;
-        nChainTx = 0;
-        nStatus = BlockStatus();
-        nSequenceId = 0;
-        nTimeMax = 0;
-
-        nVersion = 0;
-        hashMerkleRoot = uint256();
-        nTime = 0;
-        nTimeReceived = 0;
-        nBits = 0;
-        nNonce = 0;
-    }
-
-    CBlockIndex() { SetNull(); }
-
-    CBlockIndex(const CBlockHeader &block) {
-        SetNull();
-
-        nVersion = block.nVersion;
-        hashMerkleRoot = block.hashMerkleRoot;
-        nTime = block.nTime;
-        // Default to block time if nTimeReceived is never set, which
-        // in effect assumes that this block is honestly mined.
-        // Note that nTimeReceived isn't written to disk, so blocks read from
-        // disk will be assumed to be honestly mined.
-        nTimeReceived = block.nTime;
-        nBits = block.nBits;
-        nNonce = block.nNonce;
-    }
-
-    CDiskBlockPos GetBlockPos() const {
-        CDiskBlockPos ret;
-        if (nStatus.hasData()) {
-            ret.nFile = nFile;
-            ret.nPos = nDataPos;
-        }
-        return ret;
-    }
-
-    CDiskBlockPos GetUndoPos() const {
-        CDiskBlockPos ret;
-        if (nStatus.hasUndo()) {
-            ret.nFile = nFile;
-            ret.nPos = nUndoPos;
-        }
-        return ret;
-    }
-
-    CBlockHeader GetBlockHeader() const {
-        CBlockHeader block;
-        block.nVersion = nVersion;
-        if (pprev) {
-            block.hashPrevBlock = pprev->GetBlockHash();
-        }
-        block.hashMerkleRoot = hashMerkleRoot;
-        block.nTime = nTime;
-        block.nBits = nBits;
-        block.nNonce = nNonce;
-        return block;
-    }
-
-    uint256 GetBlockHash() const { return *phashBlock; }
-
-    int64_t GetBlockTime() const { return int64_t(nTime); }
-
-    int64_t GetBlockTimeMax() const { return int64_t(nTimeMax); }
-
-    int64_t GetHeaderReceivedTime() const { return nTimeReceived; }
-
-    int64_t GetReceivedTimeDiff() const {
-        return GetHeaderReceivedTime() - GetBlockTime();
-    }
-
-    enum { nMedianTimeSpan = 11 };
-
-    int64_t GetMedianTimePast() const {
-        int64_t pmedian[nMedianTimeSpan];
-        int64_t *pbegin = &pmedian[nMedianTimeSpan];
-        int64_t *pend = &pmedian[nMedianTimeSpan];
-
-        const CBlockIndex *pindex = this;
-        for (int i = 0; i < nMedianTimeSpan && pindex;
-             i++, pindex = pindex->pprev) {
-            *(--pbegin) = pindex->GetBlockTime();
-        }
-
-        std::sort(pbegin, pend);
-        return pbegin[(pend - pbegin) / 2];
-    }
-
-    std::string ToString() const {
-        return strprintf(
-            "CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)", pprev,
-            nHeight, hashMerkleRoot.ToString(), GetBlockHash().ToString());
-    }
-
-    //! Check whether this block index entry is valid up to the passed validity
-    //! level.
-    bool IsValid(enum BlockValidity nUpTo = BlockValidity::TRANSACTIONS) const {
-        return nStatus.isValid(nUpTo);
-    }
-
-    //! Raise the validity level of this block index entry.
-    //! Returns true if the validity was changed.
-    bool RaiseValidity(enum BlockValidity nUpTo) {
-        // Only validity flags allowed.
-        if (nStatus.isInvalid()) {
-            return false;
-        }
-
-        if (nStatus.getValidity() >= nUpTo) {
-            return false;
-        }
-
-        nStatus = nStatus.withValidity(nUpTo);
-        return true;
-    }
-
-    //! Build the skiplist pointer for this entry.
-    void BuildSkip();
-
-    //! Efficiently find an ancestor of this block.
-    CBlockIndex *GetAncestor(int height);
-    const CBlockIndex *GetAncestor(int height) const;
-};
-
 /**
  * Maintain a map of CBlockIndex for all known headers.
  */
@@ -262,7 +59,11 @@
 const CBlockIndex *LastCommonAncestor(const CBlockIndex *pa,
                                       const CBlockIndex *pb);
 
-/** Used to marshal pointers into hashes for db storage. */
+/**
+ * Used to marshal pointers into hashes for db storage.
+ * TODO: Once CDiskBlockIndex is removed chain.h should
+ * use a forward declaration for CBlockIndex.
+*/
 class CDiskBlockIndex : public CBlockIndex {
 public:
     uint256 hashPrev;
diff --git a/src/miner.cpp b/src/miner.cpp
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -6,7 +6,7 @@
 #include "miner.h"
 
 #include "amount.h"
-#include "chain.h"
+#include "blockindex.h"
 #include "chainparams.h"
 #include "coins.h"
 #include "config.h"
diff --git a/src/pow.cpp b/src/pow.cpp
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -7,7 +7,7 @@
 #include "pow.h"
 
 #include "arith_uint256.h"
-#include "chain.h"
+#include "blockindex.h"
 #include "chainparams.h"
 #include "config.h"
 #include "consensus/activation.h"
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -6,6 +6,7 @@
 #include "rpc/blockchain.h"
 
 #include "amount.h"
+#include "blockindex.h"
 #include "chain.h"
 #include "chainparams.h"
 #include "checkpoints.h"
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -5,6 +5,7 @@
 
 #include "rpc/mining.h"
 #include "amount.h"
+#include "blockindex.h"
 #include "blockvalidity.h"
 #include "chain.h"
 #include "chainparams.h"
diff --git a/src/test/blockencodings_tests.cpp b/src/test/blockencodings_tests.cpp
--- a/src/test/blockencodings_tests.cpp
+++ b/src/test/blockencodings_tests.cpp
@@ -6,6 +6,7 @@
 #include "chainparams.h"
 #include "config.h"
 #include "consensus/merkle.h"
+#include "pow.h"
 #include "random.h"
 
 #include "test/test_bitcoin.h"
diff --git a/src/test/blockindex_tests.cpp b/src/test/blockindex_tests.cpp
--- a/src/test/blockindex_tests.cpp
+++ b/src/test/blockindex_tests.cpp
@@ -2,8 +2,8 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include "blockindex.h"
 #include "blockvalidity.h"
-#include "chain.h"
 #include "diskblockpos.h"
 #include "uint256.h"
 
diff --git a/src/test/pow_tests.cpp b/src/test/pow_tests.cpp
--- a/src/test/pow_tests.cpp
+++ b/src/test/pow_tests.cpp
@@ -2,6 +2,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include "blockindex.h"
 #include "chain.h"
 #include "chainparams.h"
 #include "config.h"
diff --git a/src/test/skiplist_tests.cpp b/src/test/skiplist_tests.cpp
--- a/src/test/skiplist_tests.cpp
+++ b/src/test/skiplist_tests.cpp
@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include "blockindex.h"
 #include "chain.h"
 #include "test/test_bitcoin.h"
 #include "util.h"
diff --git a/src/test/versionbits_tests.cpp b/src/test/versionbits_tests.cpp
--- a/src/test/versionbits_tests.cpp
+++ b/src/test/versionbits_tests.cpp
@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include "chain.h"
+#include "blockindex.h"
 #include "chainparams.h"
 #include "consensus/params.h"
 #include "test/test_bitcoin.h"
diff --git a/src/txdb.h b/src/txdb.h
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -7,7 +7,6 @@
 #define BITCOIN_TXDB_H
 
 #include "blockfileinfo.h"
-#include "chain.h"
 #include "coins.h"
 #include "dbwrapper.h"
 #include "diskblockpos.h"
diff --git a/src/txdb.cpp b/src/txdb.cpp
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -5,6 +5,7 @@
 
 #include "txdb.h"
 
+#include "chain.h"
 #include "chainparams.h"
 #include "hash.h"
 #include "init.h"
diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -12,7 +12,9 @@
 #endif
 
 #include "amount.h"
+#include "arith_uint256.h"
 #include "blockfileinfo.h"
+#include "chain.h"
 #include "coins.h"
 #include "consensus/consensus.h"
 #include "diskblockpos.h"
diff --git a/src/validation.cpp b/src/validation.cpp
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -7,6 +7,7 @@
 #include "validation.h"
 
 #include "arith_uint256.h"
+#include "blockindex.h"
 #include "blockindexworkcomparator.h"
 #include "blockvalidity.h"
 #include "chainparams.h"
diff --git a/src/versionbits.h b/src/versionbits.h
--- a/src/versionbits.h
+++ b/src/versionbits.h
@@ -5,9 +5,11 @@
 #ifndef BITCOIN_CONSENSUS_VERSIONBITS
 #define BITCOIN_CONSENSUS_VERSIONBITS
 
-#include "chain.h"
+#include "consensus/params.h"
 #include <map>
 
+class CBlockIndex;
+
 /** What block version to use for new blocks (pre versionbits) */
 static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;
 /** What bits to set in version for versionbits blocks */
diff --git a/src/versionbits.cpp b/src/versionbits.cpp
--- a/src/versionbits.cpp
+++ b/src/versionbits.cpp
@@ -4,6 +4,7 @@
 
 #include "versionbits.h"
 
+#include "blockindex.h"
 #include "consensus/params.h"
 
 const struct BIP9DeploymentInfo
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
--- a/src/wallet/rpcdump.cpp
+++ b/src/wallet/rpcdump.cpp
@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "base58.h"
+#include "blockindex.h"
 #include "chain.h"
 #include "config.h"
 #include "core_io.h"
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4,6 +4,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "amount.h"
+#include "blockindex.h"
 #include "chain.h"
 #include "chainparams.h" // for GetConsensus.
 #include "config.h"
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -5,6 +5,7 @@
 
 #include "wallet/wallet.h"
 
+#include "blockindex.h"
 #include "chain.h"
 #include "checkpoints.h"
 #include "config.h"