Ruby is a popular, flexible and intuitive object-oriented programming language. This popularity can, in no small part, be attributed to the introduction and wide adoption of the Ruby on Rails framework. It is difficult, however, to get the most out of Ruby on Rails without first learning something about programming in Ruby, and this is where Ruby Essentials comes in. Ruby Essentials is a free on-line book designed to provide a concise and easy to follow guide to learning Ruby. Everything from installing Ruby and the basics of the language through to topics such as arrays, file handling and object-oriented programming are covered, all combined with easy to understand code examples which serve to bridge the gap between theory and practice. Ruby Essentials is intended to be of equal use both to those experienced in other programming languages and to novices who have chosen Ruby as their first programming language.