Domain-Driven Design by Eric Evans
This is considered The book to read if you want to learn DDD, however it can be a bit difficult to read, if your native language isn`t English. I had to read some paragraphs a few times before I understood the meaning.
The great thing about the book is that it really goes into the depths of DDD, but the downside is that it doesn`t really have enough code examples. So if you are a .NET developer then you should also check out the book by Jimmy Nilsson.
If you need help on DDD, then you can vist this DDD Group