diff --git a/src/pubkey.h b/src/pubkey.h
--- a/src/pubkey.h
+++ b/src/pubkey.h
@@ -95,6 +95,7 @@
 
     //! Simple read-only vector-like interface to the pubkey data.
     unsigned int size() const { return GetLen(vch[0]); }
+    const uint8_t *data() const { return vch; }
     const uint8_t *begin() const { return vch; }
     const uint8_t *end() const { return vch + size(); }
     const uint8_t &operator[](unsigned int pos) const { return vch[pos]; }
diff --git a/src/script/sign.h b/src/script/sign.h
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -6,8 +6,13 @@
 #ifndef BITCOIN_SCRIPT_SIGN_H
 #define BITCOIN_SCRIPT_SIGN_H
 
+#include <hash.h>
+#include <pubkey.h>
 #include <script/interpreter.h>
 #include <script/sighashtype.h>
+#include <streams.h>
+
+#include <boost/optional.hpp>
 
 class CKey;
 class CKeyID;
@@ -89,6 +94,502 @@
     void MergeSignatureData(SignatureData sigdata);
 };
 
+// Magic bytes
+static constexpr uint8_t PSBT_MAGIC_BYTES[5] = {'p', 's', 'b', 't', 0xff};
+
+// Global types
+static constexpr uint8_t PSBT_GLOBAL_UNSIGNED_TX = 0x00;
+
+// Input types
+static constexpr uint8_t PSBT_IN_UTXO = 0x00;
+static constexpr uint8_t PSBT_IN_PARTIAL_SIG = 0x02;
+static constexpr uint8_t PSBT_IN_SIGHASH = 0x03;
+static constexpr uint8_t PSBT_IN_REDEEMSCRIPT = 0x04;
+static constexpr uint8_t PSBT_IN_BIP32_DERIVATION = 0x06;
+static constexpr uint8_t PSBT_IN_SCRIPTSIG = 0x07;
+
+// Output types
+static constexpr uint8_t PSBT_OUT_REDEEMSCRIPT = 0x00;
+static constexpr uint8_t PSBT_OUT_BIP32_DERIVATION = 0x02;
+
+// The separator is 0x00. Reading this in means that the unserializer can
+// interpret it as a 0 length key which indicates that this is the separator.
+// The separator has no value.
+static constexpr uint8_t PSBT_SEPARATOR = 0x00;
+
+// Takes a stream and multiple arguments and serializes them into a vector and
+// then into the stream The resulting output into the stream has the total
+// serialized length of all of the objects followed by all objects concatenated
+// with each other.
+template <typename Stream, typename... X>
+void SerializeToVector(Stream &s, const X &... args) {
+    std::vector<uint8_t> ret;
+    CVectorWriter ss(SER_NETWORK, PROTOCOL_VERSION, ret, 0);
+    SerializeMany(ss, args...);
+    s << ret;
+}
+
+// Takes a stream and multiple arguments and unserializes them first as a vector
+// then each object individually in the order provided in the arguments
+template <typename Stream, typename... X>
+void UnserializeFromVector(Stream &s, X &... args) {
+    std::vector<uint8_t> data;
+    s >> data;
+    CDataStream ss(data, SER_NETWORK, PROTOCOL_VERSION);
+    UnserializeMany(ss, args...);
+    if (!ss.eof()) {
+        throw std::ios_base::failure("Size of value was not the stated size");
+    }
+}
+
+// Deserialize HD keypaths into a map
+template <typename Stream>
+void DeserializeHDKeypaths(
+    Stream &s, const std::vector<uint8_t> &key,
+    std::map<CPubKey, std::vector<uint32_t>> &hd_keypaths) {
+    // Make sure that the key is the size of pubkey + 1
+    if (key.size() != CPubKey::PUBLIC_KEY_SIZE + 1 &&
+        key.size() != CPubKey::COMPRESSED_PUBLIC_KEY_SIZE + 1) {
+        throw std::ios_base::failure(
+            "Size of key was not the expected size for the type BIP32 keypath");
+    }
+    // Read in the pubkey from key
+    CPubKey pubkey(key.begin() + 1, key.end());
+    if (!pubkey.IsFullyValid()) {
+        throw std::ios_base::failure("Invalid pubkey");
+    }
+    if (hd_keypaths.count(pubkey) > 0) {
+        throw std::ios_base::failure(
+            "Duplicate Key, pubkey derivation path already provided");
+    }
+
+    // Read in key path
+    uint64_t value_len = ReadCompactSize(s);
+    std::vector<uint32_t> keypath;
+    for (unsigned int i = 0; i < value_len; i += sizeof(uint32_t)) {
+        uint32_t index;
+        s >> index;
+        keypath.push_back(index);
+    }
+
+    // Add to map
+    hd_keypaths.emplace(pubkey, keypath);
+}
+
+// Serialize HD keypaths to a stream from a map
+template <typename Stream>
+void SerializeHDKeypaths(
+    Stream &s, const std::map<CPubKey, std::vector<uint32_t>> &hd_keypaths,
+    uint8_t type) {
+    for (auto keypath_pair : hd_keypaths) {
+        SerializeToVector(s, type, MakeSpan(keypath_pair.first));
+        WriteCompactSize(s, keypath_pair.second.size() * sizeof(uint32_t));
+        for (auto &path : keypath_pair.second) {
+            s << path;
+        }
+    }
+}
+
+/** A structure for PSBTs which contain per-input information */
+struct PSBTInput {
+    CTxOut utxo;
+    CScript redeem_script;
+    CScript final_script_sig;
+    std::map<CPubKey, std::vector<uint32_t>> hd_keypaths;
+    std::map<CKeyID, SigPair> partial_sigs;
+    std::map<std::vector<uint8_t>, std::vector<uint8_t>> unknown;
+    SigHashType sighash_type = SigHashType(0);
+
+    bool IsNull() const;
+    PSBTInput() {}
+
+    template <typename Stream> inline void Serialize(Stream &s) const {
+        // Write the utxo
+        SerializeToVector(s, PSBT_IN_UTXO);
+        SerializeToVector(s, utxo);
+
+        if (final_script_sig.empty()) {
+            // Write any partial signatures
+            for (auto sig_pair : partial_sigs) {
+                SerializeToVector(s, PSBT_IN_PARTIAL_SIG,
+                                  MakeSpan(sig_pair.second.first));
+                s << sig_pair.second.second;
+            }
+
+            // Write the sighash type
+            if (sighash_type.getRawSigHashType() != 0) {
+                SerializeToVector(s, PSBT_IN_SIGHASH);
+                SerializeToVector(s, sighash_type);
+            }
+
+            // Write the redeem script
+            if (!redeem_script.empty()) {
+                SerializeToVector(s, PSBT_IN_REDEEMSCRIPT);
+                s << redeem_script;
+            }
+
+            // Write any hd keypaths
+            SerializeHDKeypaths(s, hd_keypaths, PSBT_IN_BIP32_DERIVATION);
+        }
+
+        // Write script sig
+        if (!final_script_sig.empty()) {
+            SerializeToVector(s, PSBT_IN_SCRIPTSIG);
+            s << final_script_sig;
+        }
+
+        // Write unknown things
+        for (auto &entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        s << PSBT_SEPARATOR;
+    }
+
+    template <typename Stream> inline void Unserialize(Stream &s) {
+        // Read loop
+        while (!s.empty()) {
+            // Read
+            std::vector<uint8_t> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed
+            // (except for separator)
+            if (key.empty()) {
+                return;
+            }
+
+            // First byte of key is the type
+            uint8_t type = key[0];
+
+            // Do stuff based on type
+            switch (type) {
+                case PSBT_IN_UTXO:
+                    if (!utxo.IsNull()) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, input utxo already provided");
+                    }
+                    UnserializeFromVector(s, utxo);
+                    break;
+                case PSBT_IN_PARTIAL_SIG: {
+                    // Make sure that the key is the size of pubkey + 1
+                    if (key.size() != CPubKey::PUBLIC_KEY_SIZE + 1 &&
+                        key.size() != CPubKey::COMPRESSED_PUBLIC_KEY_SIZE + 1) {
+                        throw std::ios_base::failure(
+                            "Size of key was not the expected size for the "
+                            "type partial signature pubkey");
+                    }
+                    // Read in the pubkey from key
+                    CPubKey pubkey(key.begin() + 1, key.end());
+                    if (!pubkey.IsFullyValid()) {
+                        throw std::ios_base::failure("Invalid pubkey");
+                    }
+                    if (partial_sigs.count(pubkey.GetID()) > 0) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, input partial signature for pubkey "
+                            "already provided");
+                    }
+
+                    // Read in the signature from value
+                    std::vector<uint8_t> sig;
+                    s >> sig;
+
+                    // Add to list
+                    partial_sigs.emplace(pubkey.GetID(),
+                                         SigPair(pubkey, std::move(sig)));
+                    break;
+                }
+                case PSBT_IN_SIGHASH:
+                    if (sighash_type.getRawSigHashType() != 0) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, input sighash type already "
+                            "provided");
+                    }
+                    UnserializeFromVector(s, sighash_type);
+                    break;
+                case PSBT_IN_REDEEMSCRIPT: {
+                    if (!redeem_script.empty()) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, input redeemScript already "
+                            "provided");
+                    }
+                    s >> redeem_script;
+                    break;
+                }
+                case PSBT_IN_BIP32_DERIVATION: {
+                    DeserializeHDKeypaths(s, key, hd_keypaths);
+                    break;
+                }
+                case PSBT_IN_SCRIPTSIG: {
+                    if (!final_script_sig.empty()) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, input final scriptSig already "
+                            "provided");
+                    }
+                    s >> final_script_sig;
+                    break;
+                }
+                // Unknown stuff
+                default:
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, key for unknown value already "
+                            "provided");
+                    }
+                    // Read in the value
+                    std::vector<uint8_t> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                    break;
+            }
+        }
+    }
+
+    template <typename Stream> PSBTInput(deserialize_type, Stream &s) {
+        Unserialize(s);
+    }
+};
+
+/** A structure for PSBTs which contains per output information */
+struct PSBTOutput {
+    CScript redeem_script;
+    std::map<CPubKey, std::vector<uint32_t>> hd_keypaths;
+    std::map<std::vector<uint8_t>, std::vector<uint8_t>> unknown;
+
+    bool IsNull() const;
+    PSBTOutput() {}
+
+    template <typename Stream> inline void Serialize(Stream &s) const {
+        // Write the redeem script
+        if (!redeem_script.empty()) {
+            SerializeToVector(s, PSBT_OUT_REDEEMSCRIPT);
+            s << redeem_script;
+        }
+
+        // Write any hd keypaths
+        SerializeHDKeypaths(s, hd_keypaths, PSBT_OUT_BIP32_DERIVATION);
+
+        // Write unknown things
+        for (auto &entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        s << PSBT_SEPARATOR;
+    }
+
+    template <typename Stream> inline void Unserialize(Stream &s) {
+        // Read loop
+        while (!s.empty()) {
+            // Read
+            std::vector<uint8_t> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed
+            // (except for separator)
+            if (key.empty()) {
+                return;
+            }
+
+            // First byte of key is the type
+            uint8_t type = key[0];
+
+            // Do stuff based on type
+            switch (type) {
+                case PSBT_OUT_REDEEMSCRIPT: {
+                    if (!redeem_script.empty()) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, output redeemScript already "
+                            "provided");
+                    }
+                    s >> redeem_script;
+                    break;
+                }
+                case PSBT_OUT_BIP32_DERIVATION: {
+                    DeserializeHDKeypaths(s, key, hd_keypaths);
+                    break;
+                }
+                // Unknown stuff
+                default: {
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, key for unknown value already "
+                            "provided");
+                    }
+                    // Read in the value
+                    std::vector<uint8_t> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                    break;
+                }
+            }
+        }
+    }
+
+    template <typename Stream> PSBTOutput(deserialize_type, Stream &s) {
+        Unserialize(s);
+    }
+};
+
+/** A version of CTransaction with the PSBT format*/
+struct PartiallySignedTransaction {
+    boost::optional<CMutableTransaction> tx;
+    std::vector<PSBTInput> inputs;
+    std::vector<PSBTOutput> outputs;
+    std::map<std::vector<uint8_t>, std::vector<uint8_t>> unknown;
+
+    bool IsNull() const;
+    PartiallySignedTransaction() {}
+    PartiallySignedTransaction(const PartiallySignedTransaction &psbt_in)
+        : tx(psbt_in.tx), inputs(psbt_in.inputs), outputs(psbt_in.outputs),
+          unknown(psbt_in.unknown) {}
+
+    // Only checks if they refer to the same transaction
+    friend bool operator==(const PartiallySignedTransaction &a,
+                           const PartiallySignedTransaction &b) {
+        return a.tx->GetHash() == b.tx->GetHash();
+    }
+    friend bool operator!=(const PartiallySignedTransaction &a,
+                           const PartiallySignedTransaction &b) {
+        return !(a == b);
+    }
+
+    template <typename Stream> inline void Serialize(Stream &s) const {
+
+        // magic bytes
+        s << PSBT_MAGIC_BYTES;
+
+        // unsigned tx flag
+        SerializeToVector(s, PSBT_GLOBAL_UNSIGNED_TX);
+
+        // Write serialized tx to a stream
+        SerializeToVector(s, *tx);
+
+        // Write the unknown things
+        for (auto &entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        // Separator
+        s << PSBT_SEPARATOR;
+
+        // Write inputs
+        for (const PSBTInput &input : inputs) {
+            s << input;
+        }
+        // Write outputs
+        for (const PSBTOutput &output : outputs) {
+            s << output;
+        }
+    }
+
+    template <typename Stream> inline void Unserialize(Stream &s) {
+        // Read the magic bytes
+        uint8_t magic[5];
+        s >> magic;
+        if (!std::equal(magic, magic + 5, PSBT_MAGIC_BYTES)) {
+            throw std::ios_base::failure("Invalid PSBT magic bytes");
+        }
+
+        // Read global data
+        while (!s.empty()) {
+            // Read
+            std::vector<uint8_t> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed
+            // (except for separator)
+            if (key.empty()) {
+                break;
+            }
+
+            // First byte of key is the type
+            uint8_t type = key[0];
+
+            // Do stuff based on type
+            switch (type) {
+                case PSBT_GLOBAL_UNSIGNED_TX: {
+                    if (tx) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, unsigned tx already provided");
+                    }
+                    CMutableTransaction mtx;
+                    UnserializeFromVector(s, mtx);
+                    tx = std::move(mtx);
+                    // Make sure that all scriptSigs and scriptWitnesses are
+                    // empty
+                    for (const CTxIn &txin : tx->vin) {
+                        if (!txin.scriptSig.empty()) {
+                            throw std::ios_base::failure(
+                                "Unsigned tx does not have empty scriptSigs "
+                                "and scriptWitnesses.");
+                        }
+                    }
+                    break;
+                }
+                // Unknown stuff
+                default: {
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure(
+                            "Duplicate Key, key for unknown value already "
+                            "provided");
+                    }
+                    // Read in the value
+                    std::vector<uint8_t> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                }
+            }
+        }
+
+        // Make sure that we got an unsigned tx
+        if (!tx) {
+            throw std::ios_base::failure(
+                "No unsigned transcation was provided");
+        }
+
+        // Read input data
+        size_t i = 0;
+        while (!s.empty() && i < tx->vin.size()) {
+            PSBTInput input;
+            s >> input;
+            inputs.push_back(input);
+            ++i;
+        }
+        // Make sure that the number of inputs matches the number of inputs in
+        // the transaction
+        if (inputs.size() != tx->vin.size()) {
+            throw std::ios_base::failure("Inputs provided does not match the "
+                                         "number of inputs in transaction.");
+        }
+
+        // Read output data
+        i = 0;
+        while (!s.empty() && i < tx->vout.size()) {
+            PSBTOutput output;
+            s >> output;
+            outputs.push_back(output);
+            ++i;
+        }
+        // Make sure that the number of outputs matches the number of outputs in
+        // the transaction
+        if (outputs.size() != tx->vout.size()) {
+            throw std::ios_base::failure("Outputs provided does not match the "
+                                         "number of outputs in transaction.");
+        }
+    }
+
+    template <typename Stream>
+    PartiallySignedTransaction(deserialize_type, Stream &s) {
+        Unserialize(s);
+    }
+};
+
 /** Produce a script signature using a generic signature creator. */
 bool ProduceSignature(const SigningProvider &provider,
                       const BaseSignatureCreator &creator,
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -400,3 +400,16 @@
 
 const BaseSignatureCreator &DUMMY_SIGNATURE_CREATOR = DummySignatureCreator();
 const SigningProvider &DUMMY_SIGNING_PROVIDER = SigningProvider();
+
+bool PartiallySignedTransaction::IsNull() const {
+    return !tx && inputs.empty() && outputs.empty() && unknown.empty();
+}
+
+bool PSBTInput::IsNull() const {
+    return utxo.IsNull() && partial_sigs.empty() && unknown.empty() &&
+           hd_keypaths.empty() && redeem_script.empty();
+}
+
+bool PSBTOutput::IsNull() const {
+    return redeem_script.empty() && hd_keypaths.empty() && unknown.empty();
+}