Middleman is distributed using the RubyGems package manager. This means you will need both the Ruby language runtime installed and RubyGems to begin using Middleman.

Mac OS X comes prepackaged with both Ruby and Rubygems, however, some of the Middleman's dependencies need to be compiled during installation and on OS X that requires Xcode Command Line Tools. Xcode can be installed from the terminal:

$ xcode-select --install

Once you have Ruby and RubyGems up and running, execute the following from the command line:

$ gem install middleman

This will install Middleman, its dependencies and the command-line tools for using Middleman.

The installation process will add one new command to your environment, with 3 useful features:

$ middleman init
$ middleman server
$ middleman build

The uses of each of these commands will be covered in the next section, Start a New Site.