You can download the latest version of Ruby at http://www.ruby-lang.org/en/downloads/. Be sure to download the binaries (not merely the source code). Windows users have the option of installing Ruby using the Ruby Installer, available at http://www.rubyinstaller.org/. There are also several alternative implementations of Ruby, the most established of which is JRuby. You can find information on where to download these implementations in Appendix D.