Plone is built on top of Zope and the Content Management Framework (CMF). To understand Plone, you have to understand Zope and the CMF as the underlying architecture. For this reason, I'll explain these two items and how they integrate with Plone in this section.

Zope is a powerful and flexible open-source Web application server developed by Zope Corporation (http://www.zope.org). Originally, Zope was developed as a stand-alone CMS, but over time it didn't satisfy the needs of its users. Then Zope Corporation developed the CMF an open-source project. The CMF provides developers with the tools necessary to create complex CMSs; it enables workflow, provides site skinning, and offers other functions.

The CMF is a framework for a system; in other words, it provides the tools for developers to build a product, rather than just providing an out-of-the-box system that users can use immediately. Plone takes this and many other features and improves upon them to provide the user with a high-quality product. Plone is a layer on top of the CMF, which is an application running on top of Zope. Understanding the CMF is key to understanding Plone. Most administration functions require the use of Zope's administration interface, and developing Plone requires an understanding of Zope and its objects.

This book doesn't go into depth about Zope; rather, it gives you enough information to complete tasks in Plone. Just reading this book will give you enough information to customize and modify almost anything you want in Plone. For more information on Zope, I recommend The Zope Book. Originally published by New Riders, it has since been placed online and is updated by community members. It's available free online at http://www.zope.org/Documentation/Books/ZopeBook/2_6Edition.

Both Zope and the CMF are key technologies that Plone needs; without them, Plone wouldn't exist. The Plone team owes a great deal of thanks to everyone at Zope Corporation for having the vision to create and then offer both Zope and the CMF as open source. The list of people I'd like to thank there and in the CMF communities is long. Thank you, everyone involved.