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+WINDOWS BUILD NOTES
+====================
+
+Below are some notes on how to build Bitcoin Core for Windows.
+
+Most developers use cross-compilation from Ubuntu to build executables for
+Windows. This is also used to build the release binaries.
+
+Building on Ubuntu Trusty 14.04 is recommended.
+At the time of writing the Windows Subsystem for Linux installs Ubuntu Xenial 16.04. The default cross
+compiler package for Ubuntu Xenial does not produce working executables for some of the bitcoin applications.
+It is possible to build on Ubuntu Xenial by installing the cross compiler packages from
+Ubuntu Zesty, see the steps below.
+Building on Ubuntu Zesty 17.04 up to 17.10 has been verified to work.
+
+While there are potentially a number of ways to build on Windows (for example using msys / mingw-w64),
+using the Windows Subsystem For Linux is the most straightforward. If you are building with
+another method, please contribute the instructions here for others who are running versions
+of Windows that are not compatible with the Windows Subsystem for Linux.
+
+Compiling with Windows Subsystem For Linux
+-------------------------------------------
+
+With Windows 10, Microsoft has released a new feature named the [Windows
+Subsystem for Linux (WSL)](https://msdn.microsoft.com/commandline/wsl/about). This
+feature allows you to run a bash shell directly on Windows in an Ubuntu-based
+environment. Within this environment you can cross compile for Windows without
+the need for a separate Linux VM or server.
+
+This feature is not supported in versions of Windows prior to Windows 10 or on
+Windows Server SKUs. In addition, it is available [only for 64-bit versions of
+Windows](https://msdn.microsoft.com/en-us/commandline/wsl/install_guide).
+
+For Windows 10 systems with the Fall Creators Update applied (version >= 16215.0) use the Windows Store
+to install Ubuntu. Search for "Linux" in the Windows Store and install the free "Ubuntu" application.
+Full instructions are available on the above link.
+
+To get the bash shell, you must first activate the feature in Windows.
+
+1. Turn on Developer Mode
+  * Open Settings -> Update and Security -> For developers
+  * Select the Developer Mode radio button
+  * Restart if necessary
+2. Enable the Windows Subsystem for Linux feature
+  * From Start, search for "Turn Windows features on or off" (type 'turn')
+  * Select Windows Subsystem for Linux (beta)
+  * Click OK
+  * Restart if necessary
+3. Complete Installation
+  * Open a cmd prompt and type "bash"
+  * Accept the license
+  * Create a new UNIX user account (this is a separate account from your Windows account)
+
+After the bash shell is active, you can follow the instructions below, starting
+with the "Cross-compilation" section. Compiling the 64-bit version is
+recommended but it is possible to compile the 32-bit version.
+
+Cross-compilation
+-------------------
+
+These steps can be performed on, for example, an Ubuntu VM. The depends system
+will also work on other Linux distributions, however the commands for
+installing the toolchain will be different.
+
+First, install the general dependencies:
+
+    sudo apt install build-essential libtool autotools-dev automake pkg-config bsdmainutils curl git
+
+A host toolchain (`build-essential`) is necessary because some dependency
+packages (such as `protobuf`) need to build host utilities that are used in the
+build process.
+
+See also: [dependencies.md](dependencies.md).
+
+## Building for 64-bit Windows
+
+The first step is to install the mingw-w64 cross-compilation tool chain. Due to different Ubuntu
+packages for each distribution and problems with the Xenial packages the steps for each are different.
+
+Common steps to install mingw32 cross compiler tool chain:
+
+    sudo apt install g++-mingw-w64-x86-64
+
+Ubuntu Trusty 14.04:
+
+    No further steps required
+
+Ubuntu Xenial 16.04 and Windows Subsystem for Linux <sup>[1](#footnote1),[2](#footnote2)</sup>:
+
+    sudo apt install software-properties-common
+    sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu zesty universe"
+    sudo apt update
+    sudo apt upgrade
+    sudo update-alternatives --config x86_64-w64-mingw32-g++ # Set the default mingw32 g++ compiler option to posix.
+
+Ubuntu Zesty 17.04 <sup>[2](#footnote2)</sup>:
+
+    sudo update-alternatives --config x86_64-w64-mingw32-g++ # Set the default mingw32 g++ compiler option to posix.
+
+Once the tool chain is installed the build steps are common:
+
+    PATH=$(echo "$PATH" | sed -e 's/:\/mnt.*//g') # strip out problematic Windows %PATH% imported var
+    cd depends
+    make HOST=x86_64-w64-mingw32
+    cd ..
+    ./autogen.sh # not required when building from tarball
+    CONFIG_SITE=$PWD/depends/x86_64-w64-mingw32/share/config.site ./configure --prefix=/
+    make
+
+## Building for 32-bit Windows
+
+To build executables for Windows 32-bit, install the following dependencies:
+
+    sudo apt install g++-mingw-w64-i686 mingw-w64-i686-dev
+
+For Ubuntu Xenial 16.04, Ubuntu Zesty 17.04 and Windows Subsystem for Linux <sup>[2](#footnote2)</sup>:
+
+    sudo update-alternatives --config i686-w64-mingw32-g++  # Set the default mingw32 g++ compiler option to posix.
+
+Then build using:
+
+    PATH=$(echo "$PATH" | sed -e 's/:\/mnt.*//g') # strip out problematic Windows %PATH% imported var
+    cd depends
+    make HOST=i686-w64-mingw32
+    cd ..
+    ./autogen.sh # not required when building from tarball
+    CONFIG_SITE=$PWD/depends/i686-w64-mingw32/share/config.site ./configure --prefix=/
+    make
+
+## Depends system
+
+For further documentation on the depends system see [README.md](../depends/README.md) in the depends directory.
+
+Installation
+-------------
+
+After building using the Windows subsystem it can be useful to copy the compiled
+executables to a directory on the windows drive in the same directory structure
+as they appear in the release `.zip` archive. This can be done in the following
+way. This will install to `c:\workspace\bitcoin`, for example:
+
+    make install DESTDIR=/mnt/c/workspace/bitcoin
+
+Footnotes
+---------
+
+<a name="footnote1">1</a>: There is currently a bug in the 64 bit mingw-w64 cross compiler packaged for WSL/Ubuntu Xenial 16.04 that
+causes two of the bitcoin executables to crash shortly after start up. The bug is related to the
+-fstack-protector-all g++ compiler flag which is used to mitigate buffer overflows.
+Installing the mingw-w64 packages from the Ubuntu 17 distribution solves the issue, however, this is not
+an officially supported approach and it's only recommended if you are prepared to reinstall WSL/Ubutntu should
+something break.
+
+<a name="footnote2">2</a>: Starting from Ubuntu Xenial 16.04 both the 32 and 64 bit mingw-w64 packages install two different
+compiler options to allow a choice between either posix or win32 threads. The default option is win32 threads which is the more
+efficient since it will result in binary code that links directly with the Windows kernel32.lib. Unfortunately, the headers
+required to support win32 threads conflict with some of the classes in the C++11 standard library in particular std::mutex.
+It's not possible to build the bitcoin code using the win32 version of the mingw-w64 cross compilers (at least not without
+modifying headers in the bitcoin source code).