In 2014, after two years of reading about and working with Domain-Driven Design, Carlos and Christian, friends and workmates, traveled to Berlin to participate in Vaughn Vernon's Implementing Domain-Driven Design Workshop. The training was fantastic, and all the concepts that were swirling around in their minds prior to the trip suddenly became very real. However, they were the only two PHP developers in a room full of Java and .NET developers. Around the same time, php[tek], an annual PHP conference, opened its call for papers, and Carlos sent one about Hexagonal Architecture. His talk was rejected, but Eli White — of musketeers.me and php[architect] fame — got in touch with him a month later wondering if he was interested in writing an article about Hexagonal Architecture for the magazine php[architect]. So in June 2014, Hexagonal Architecture with PHP was published. That article, which you'll find in the Appendix, was the origin of this book. In late 2014, Carlos and Christian talked about extending the article and sharing all their knowledge of and experience in applying Domain-Driven Design in production. They were very excited about the idea behind the book: helping the PHP community delve into Domain-Driven Design from a practical approach. At that time, concepts such as Rich Domain Models and framework-agnostic applications weren't so common in the PHP community. So in December 2014, the first commit to the GitHub book repository was pushed.