Brief article explains main aspects, by Hal Fulton.

By Hal Fulton; Sams Publishing, 2001, ISBN 0672320835. Assumes reader knows programming, by teacher and programmer, Uses code samples to focus on how to use Ruby for specific uses, alone or with other languages.

David Flanagan, Yukihiro Matz Matsumoto, why the lucky stiff; O'Reilly Media, 2008, ISBN 9780596516178. Authoritative guide, covers versions 1.9, 1.8; shows Ruby's lexical structure, primary expressions, conditionals, syntax, classes, data they manipu...

By Mark Slagell; Sams Publishing, 2002, ISBN 0672322528. Introduction to language, originally addressed an early key constraint: a lack of quality English-language documentation.

By Yukihiro "Matz" Matsumoto; O'Reilly and Associates, 2001, ISBN 0596002149. By programmer, and Ruby creator; concise broad reference guide assumes reader knows programming. [O'Reilly and Associates]

By Lucas Carlson, Leonard Richardson; O'Reilly, 2006, ISBN 0596523696. From data structures to algorithms to integrating with new technologies; when solving a problem, don't reinvent the wheel: look it up in here. O'Reilly Media.

Full online HTML text at Ruby Central, with download link. [Open Content, Open Publication License]

Interview with Programming Ruby authors, The Pragmatic Programmers. Amazon.com.

By Suresh Mahadevan; John Wiley and Sons, 2002, ISBN 047121972X. Hands-on full introduction, how to save much time, many real-world examples, how to move beyond examples to specific tasks, end-of-chapter reviews, exercises.

By Chris Pine; Pragmatic Bookshelf, 2006, ISBN 0976694042. Engaging beginner introduction to programming, via Ruby. Not only for Ruby newbies. Online version has live code samples, running input and output as a constant quality check; in English, Fran...