I came to rails knowing very little about ruby and even less about rails. This book got me started on the right foot. At the end I was able to understand how rails works, although I wasn't able to write any real programs on my own. This book assumes that you know nothing about Ruby or Rails. It's written in a clear, concise and entertaining style, and gave me a good idea how the whole rails framework functions. Agile Web Development with Rails, Third Edition is one of the more popular guides that I'm reading now. It's also a good beginner's book but it might be too difficult for complete newbies. I think I'd have much more difficulty understanding it if I hadn't read Simply Rails.