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diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
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+++ b/src/interfaces/chain.h
@@ -0,0 +1,84 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_INTERFACES_CHAIN_H
+#define BITCOIN_INTERFACES_CHAIN_H
+
+#include <memory>
+#include <string>
+#include <vector>
+
+class CScheduler;
+
+namespace interfaces {
+
+//! Interface for giving wallet processes access to blockchain state.
+class Chain
+{
+public:
+    virtual ~Chain() {}
+
+    //! Interface for querying locked chain state, used by legacy code that
+    //! assumes state won't change between calls. New code should avoid using
+    //! the Lock interface and instead call higher-level Chain methods
+    //! that return more information so the chain doesn't need to stay locked
+    //! between calls.
+    class Lock
+    {
+    public:
+        virtual ~Lock() {}
+    };
+
+    //! Return Lock interface. Chain is locked when this is called, and
+    //! unlocked when the returned interface is freed.
+    virtual std::unique_ptr<Lock> lock(bool try_lock = false) = 0;
+
+    //! Return Lock interface assuming chain is already locked. This
+    //! method is temporary and is only used in a few places to avoid changing
+    //! behavior while code is transitioned to use the Chain::Lock interface.
+    virtual std::unique_ptr<Lock> assumeLocked() = 0;
+};
+
+//! Interface to let node manage chain clients (wallets, or maybe tools for
+//! monitoring and analysis in the future).
+class ChainClient
+{
+public:
+    virtual ~ChainClient() {}
+
+    //! Register rpcs.
+    virtual void registerRpcs() = 0;
+
+    //! Check for errors before loading.
+    virtual bool verify() = 0;
+
+    //! Load saved state.
+    virtual bool load() = 0;
+
+    //! Start client execution and provide a scheduler.
+    virtual void start(CScheduler& scheduler) = 0;
+
+    //! Save state to disk.
+    virtual void flush() = 0;
+
+    //! Shut down client.
+    virtual void stop() = 0;
+};
+
+//! Return implementation of Chain interface.
+std::unique_ptr<Chain> MakeChain();
+
+//! Return implementation of ChainClient interface for a wallet client. This
+//! function will be undefined in builds where ENABLE_WALLET is false.
+//!
+//! Currently, wallets are the only chain clients. But in the future, other
+//! types of chain clients could be added, such as tools for monitoring,
+//! analysis, or fee estimation. These clients need to expose their own
+//! MakeXXXClient functions returning their implementations of the ChainClient
+//! interface.
+std::unique_ptr<ChainClient> MakeWalletClient(Chain& chain, std::vector<std::string> wallet_filenames);
+
+} // namespace interfaces
+
+#endif // BITCOIN_INTERFACES_CHAIN_H