The Handbook of Software Architecture is an ongoing project to codify the architecture of a number of interesting software-intensive systems, using the UML and Kruchten's 4+1 model view. The process of developing this handbook serves to advance our understanding of what architecture is, what it is not, how one may describe it, and how one may develop such well-formed systems. The artifacts developed in these archeological digs serve to help the corresponding development teams reason about their as-built systems and intentionally govern how to best transform them.