This is the first book I have read since university. It was proposed to me not long after I joined the company I currently work at and is one of the inspirations for the way I work and this blog.
I'm going to talk about the C# version of the book (Agile Principles, Patterns, and Practices in C#), but it also applies to the Java version (Agile Software Development: Principles, Patterns, and Practices). Both books were written by Robert C. Martin (Uncle Bob).