Constant learning and enough amount of practice help to improve programmer's level. There are numerous online courses and tutorials that do a really good job.

But what about paper sources of information? Are there any useful books for Rubyists? Though web development and new methods move at a stunning pace, books play an important role in studying process. It's not wise to call them all outdated and irrelevant.  Good books are written by true professionals in their sphere. In tutorials writers share their experience and provide invaluable theoretical material to master by practice.

So let’s have a look at Ruby library. 

Michael Hartl

Ruby on Rails Tutorial: Learn Web Development with Rails

Considered to be a must-read for programmers who start learning Ruby on Rails. The book introduces developers to the framework and important notions connected with Rails: git, bootstrap, heroku, etc.

It gives insight on how to create and deploy applications with Ruby on Rails. 

Ryan Bigg, Yehuda Katz, Steve Klabnik, Rebecca Skinner

Rails 4 in Action: Revised Edtion of Rails in Action

An introduction to Rails that explains the main steps to build apps and focuses on test-first development. 

The book helps to master Rails 4. Apart from Rails applications student will learn to create their own APIs and use RSpec and Capybara.

Ruby background is not required to read this book. 

Sandi Metz

Practical Object-Oriented Design in Ruby: An Agile Primer

The book is about how to write object-oriented code.

The guide tackles the main principles of object-oriented design. It explains how to build objects via composition, manage dependencies, implement duck types, design cost-effective tests, create simple and clear code and much more. 

Ryan Bigg

Multitenancy with Rails

The book teaches to build multi-tenanted Ruby on Rails applications (Software as a Service).

It also touches upon several programming practices like TDD, DRY, etc. The book is written as a practical study. 

Russ Olsen

Eloquent Ruby

A good book for those come from other languages and want to get introduced to Ruby. The guide helps to achieve fluency in writing Ruby code. It teaches students good, idiomatic Ruby. 

David A.Black

The Well-Grounded Rubyist

It is more a Ruby reference book dealing with everything from basic concepts to advanced dynamic principles.

The book focuses on the Ruby language (provides its thorough overview) and not Rails. 

Jim Gay

Clean Ruby

The book teaches to understand code and have it well organized. It contains clear examples and explanation of BDD and DCI.

Chad Fowler

Rails Recipes

The books gives solutions (‘recipes’) to a number of problems a Rails developer may face. It can be used as a reference book. It includes insights of members of the Rails core team and other professionals. 

The more sources of information are used to improve your Ruby skills and learn something new the better. Books present one more angle to achieve great results in programming. Keep your bookshelf filled with good books.