Design Patterns: Elements of Reusable Object-Oriented Software by Erich Gamma (Author), Richard Helm (Author), Ralph Johnson (Author), John Vlissides (Author), Grady Booch (Foreword)

This is a book on patterns used in object-oriented design. Quite a classic one! Enjoyed reading book cover to cover. It has 23 design patterns and the authors explained the intention, motivation, applicability, structure, participants, collaborations, consequences, implementation, sample code, known uses and related patterns for each. Book is not very difficult to follow.
First chapter is the introduction to design patterns. Second chapter is a case study, a document editor, through which covered 8 patterns. Third, fourth and fifth chapters covered all 23 design patterns under three subsections - creational patterns, structural pattern and behavioral patterns.
The very first pattern author introduced was a structural pattern, composite pattern. An amazing solution for the problem at hand.
A must read for a professional who deal with OOD!