The Well Grounded Rubyist is a wonderful resource and the third edition, released this August, covers Ruby 2.5. https://www.manning.com/books/the-well-grounded

The Well Grounded Rubyist is a wonderful resource and the third edition, released this August, covers Ruby 2.5. https://www.manning.com/books/the-well-grounded-rubyist-third-edition https://www.manning.com/books/the-well-grounded-rubyist-thir... * Sorry, it seems it's going to be released on January 2019. In any case, the second edition covers Ruby 2.1. It's safe to learn with that one.