Practical Object-Oriented Design in Ruby - by Sandi Metz

Any rubyist will tell you, this is a must-read for anyone starting out development in OOP or Ruby in general. Sandi Metz broke ground with this book, written in 2012.

"The first title to focus squarely on object-oriented Ruby application design, Practical Object-Oriented Design in Ruby will guide you to superior outcomes, whatever your previous Ruby experience. Novice Ruby programmers will find specific rules to live by; intermediate Ruby programmers will find valuable principles they can flexibly interpret and apply; and advanced Ruby programmers will find a common language they can use to lead development and guide their colleagues."

Try out a sample of the book below.