Domain-Driven Design: Tackling Complexity in the Heart of Software

Eric Evans's "Blue Book" introduced concepts that are hard to imagine discussing architecture without today: ubiquitous language, bounded context, aggregate, and context map. It teaches you to build a domain model together with the business and to keep your code aligned with that model.

The book is dense and at times academic, so it works best when you have already worked on a large project and run into the problems it describes. If DDD is new to you, start with Learning Domain-Driven Design.