i3 has the following dependencies:

   "min" means minimum required version
   "lkgv" means last known good version

┌──────────────┬────────┬────────┬────────────────────────────────────────┐
│ dependency   │ min.   │ lkgv   │ URL                                    │
├──────────────┼────────┼────────┼────────────────────────────────────────┤
│ pkg-config   │ 0.25   │ 0.26   │ http://pkgconfig.freedesktop.org/      │
│ libxcb       │ 1.1.93 │ 1.10   │ http://xcb.freedesktop.org/dist/       │
│ xcb-util     │ 0.3.3  │ 0.4.1  │ http://xcb.freedesktop.org/dist/       │
│ xkbcommon    │ 0.4.0  │ 0.4.0  │ http://xkbcommon.org/                  │
│ xkbcommon-x11│ 0.4.0  │ 0.4.0  │ http://xkbcommon.org/                  │
│ util-cursor³ │ 0.0.99 │ 0.0.99 │ http://xcb.freedesktop.org/dist/       │
│ libev        │ 4.0    │ 4.11   │ http://libev.schmorp.de/               │
│ yajl         │ 2.0.1  │ 2.0.4  │ http://lloyd.github.com/yajl/          │
│ asciidoc     │ 8.3.0  │ 8.6.4  │ http://www.methods.co.nz/asciidoc/     │
│ xmlto        │ 0.0.23 │ 0.0.23 │ http://www.methods.co.nz/asciidoc/     │
│ Pod::Simple² │ 3.22   │ 3.22   │ http://search.cpan.org/~dwheeler/Pod-Simple-3.23/
│ docbook-xml  │ 4.5    │ 4.5    │ http://www.methods.co.nz/asciidoc/     │
│ Xlib         │ 1.3.3  │ 1.4.3  │ http://ftp.x.org/pub/current/src/lib/  │
│ PCRE         │ 8.12   │ 8.12   │ http://www.pcre.org/                   │
│ libsn¹       │ 0.10   │ 0.12   │ http://freedesktop.org/wiki/Software/startup-notification
│ pango        │ 1.30.0 | 1.30.0 │ http://www.pango.org/                  │
│ cairo        │ 1.12.2 │ 1.12.2 │ http://cairographics.org/              │
└──────────────┴────────┴────────┴────────────────────────────────────────┘
 ¹ libsn = libstartup-notification
 ² Pod::Simple is a Perl module required for converting the testsuite
   documentation to HTML. See http://michael.stapelberg.de/cpan/#Pod::Simple
 ³ xcb-util-cursor, to be precise. Might be considered part of xcb-util, or not
   :-).

 i3bar, i3-msg, i3-input, i3-nagbar and i3-config-wizard do not introduce any
 new dependencies.

 i3-migrate-config-to-v4 and i3-dmenu-desktop are implemented in Perl, but have
 no dependencies besides Perl 5.10.

 i3-save-tree is also implemented in Perl and needs AnyEvent::I3 and JSON::XS.
 While i3-save-tree is not required for running i3 itself, it is strongly
 recommended to provide it in distribution packages.