diff --git a/INSTALL.md b/INSTALL.md
index 958ddd1..ecac726 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -1,16 +1,190 @@
-DeforaOS configure
-==================
-
-Installation notes
-------------------
-
-To install configure in `/usr/local`, just proceed this way:
-
-    $ make
-    $ make install
-
-To install it in another directory, use the `PREFIX` variable:
-
-    $ make PREFIX="/path/to/destination" install
-
-The `DESTDIR` variable is also supported for package maintainers.
+DeforaOS configure
+==================
+
+Installation notes
+------------------
+
+configure is written in C and depends on libSystem, the DeforaOS base library.
+Both are built from source. The Makefiles in this repository are already
+generated, so you do not need configure to build configure.
+
+The commands below are for Debian and Ubuntu; other systems are listed at the
+end.
+
+
+Dependencies
+------------
+
+```
+sudo apt install -y build-essential git pkg-config xsltproc docbook-xsl libxml2-utils gtk-doc-tools
+```
+
+The last four build the manual pages and a gtk-doc example in the tests. Without
+gtk-doc, `make` fails in `tests/`. Without xsltproc or docbook-xsl, the manual
+pages are silently skipped.
+
+
+Building libSystem
+------------------
+
+configure needs libSystem 0.3.2 or later. Its directories have to be built in
+this order:
+
+```
+git clone https://github.com/DeforaOS/libSystem.git
+cd libSystem
+for dir in include data src tools; do
+	(cd "$dir" && make && sudo make install) || break
+done
+cd ..
+# This should return the version of libSystem installed.
+pkg-config --modversion libSystem
+```
+
+The last command should print a version. If it does not, set
+`PKG_CONFIG_PATH` (see "Custom prefix" below).
+
+
+Building and installing configure
+---------------------------------
+
+```
+git clone https://github.com/DeforaOS/configure.git
+cd configure
+make
+sudo make install
+```
+
+This installs `configure` and `configure-update` in `/usr/local/bin`, their data in `/usr/local/share/configure`, the helper scripts used by generated
+Makefiles in `/usr/local/libexec/configure`, and the manual pages. To check it works, run a dry run from the source directory:
+
+```
+configure -n -v
+```
+
+Running the tests
+-----------------
+
+```
+(cd tests && make tests.log)
+grep -E 'PASS|FAIL' tests/tests.log
+```
+
+Note: `make tests` at the top level also runs lint and report scripts and stops
+at the first failure. `fixme.sh` currently fails because the code contains
+FIXME comments; this does not mean the build is broken.
+
+
+Custom prefix
+-------------
+
+The prefix is compiled into configure so it can find its data files, so pass the same `PREFIX` to both `make` and `make install`. For example, without root:
+
+```
+cd libSystem
+for dir in include data src tools; do
+	(cd "$dir" && make PREFIX="$HOME/.local" install) || break
+done
+
+cd ../configure
+export PKG_CONFIG_PATH="$HOME/.local/lib/pkgconfig"
+make PREFIX="$HOME/.local"
+make PREFIX="$HOME/.local" install
+```
+
+`PKG_CONFIG_PATH` is only needed while building, since the library path is recorded in the binary. Package maintainers can also stage files with
+`make DESTDIR="/tmp/staging" install`.
+
+
+Without the documentation
+-------------------------
+
+To skip the manual pages and the documentation tools, build only these
+directories instead of running `make` at the top level:
+
+```
+for dir in data src tools; do
+	(cd "$dir" && make && sudo make install) || break
+done
+```
+
+To uninstall, run `sudo make uninstall` in the same places you installed from.
+
+
+Other systems
+-------------
+
+The steps are the same, only the packages change. The generated Makefiles work
+with both GNU and BSD make.
+
+
+Fedora:
+```
+dnf install gcc make git pkgconf-pkg-config libxslt docbook-style-xsl libxml2 gtk-doc
+```
+
+Arch:
+```
+pacman -S --needed base-devel git libxslt docbook-xsl libxml2 gtk-doc
+```
+
+FreeBSD:
+```
+pkg install git pkgconf libxslt docbook-xsl gtk-doc
+```
+
+NetBSD:
+```
+pkgin install git-base pkgconf libxslt docbook-xsl gtk-doc
+```
+
+OpenBSD:
+```
+pkg_add git libxslt docbook-xsl gtk-doc
+```
+
+macOS:
+```
+brew install pkgconf libxslt docbook-xsl gtk-doc
+```
+
+On Fedora, export `PKG_CONFIG_PATH=/usr/local/lib/pkgconfig` before building
+configure. On macOS, set
+`XML_CATALOG_FILES="$(brew --prefix)/etc/xml/catalog"` so the manual pages can
+be generated.
+
+Windows is not supported natively: use WSL with the Debian or Ubuntu steps.
+configure can still generate Makefiles for Windows targets with
+`configure -O Windows`.
+
+
+Uninstalling
+------------
+
+To uninstall configure, go to the configure source directory and run:
+
+```
+cd configure
+sudo make uninstall
+```
+
+To uninstall libSystem, run `make uninstall` in each directory where it was
+installed:
+
+```
+cd ../libSystem
+for dir in include data src tools; do
+	(cd "$dir" && sudo make uninstall) || break
+done
+```
+
+If you installed with a custom prefix, use the same prefix again:
+
+```
+cd configure
+make PREFIX="$HOME/.local" uninstall
+cd ../libSystem
+for dir in include data src tools; do
+	(cd "$dir" && make PREFIX="$HOME/.local" uninstall) || break
+done
+```
\ No newline at end of file