As others have already noted, this is a seminal work on design patterns and is considered by many software professionals as a must read. It is probably a bit too complex for novices to design patterns in which case they are better off using another resource for starters (e.g.: Head First Design Patterns) and then eventually move on to this book. Head First design patterns was obviously easier to read and understand since the examples are more up to date and material is not as thorough as this book. It took me more than a month and half to read this book carefully from cover to cover. Although a lot of the patterns are discussed in depth from a theoretical level including evaluating trade-offs made with specific implementation choices, the examples in SmallTalk are out of date and not that relevant anymore but that's understandable given the publish date of this book (1994). Like some other books (e.g.: Java Concurrency in Practice), multiple readings are necessary to fully digest the material and that needs to be coupled with either independent practice of the specific implementation choices and/or other resources that have more examples of pattern implementations so as to not only reinforce understanding but also lay a solid foundation for Object Oriented Design. Most senior folks working with Object Oriented Systems typically have this book at their desk as a reference. I found one particular pattern, namely Interpreter, pretty difficult to follow. Other than that the rest of the material is readable. Having some familiarity with UML notation will help but the appendix includes explanation of the notation used in the book, so it is not a stopper if you don't have any exposure in that area. Towards the end of each chapter covering a given pattern, the authors include a section on related patterns which can be extremely helpful. This book also organizes different patterns into creational, structural and behavioral categories and also identifies which ones within a given category can supplement each other and which ones compete against each other. This book is not meant to be a comprehensive resource on design patterns and will have to be supplemented by other books. Highly recommended for anyone working with Object Oriented Systems.