What is P3P, W3C Privacy Policy Summary

What is P3P?

• Participating Web sites answer a set of multiple-choice questions creating a summary of the site's privacy practices, which can then be interpreted and displayed by P3P-enabled browsers. 
• When you use a P3P-enabled browser to visit a site participating in P3P, the browser automatically reads the site's P3P summary comparing the site's privacy practices to the privacy preferences you've set. The browser might display an alert or block transmission of certain data, such as cookies, if a Web site's practices differ from your preferences.
  

Here is the deployment guide for P3P from W3C.  This covers the development of the technical P3P, the human readable P3P and some technical details about how the code-level implementation of P3P is executed.

Here is the "how-to establish P3P at your site" document from the W3C.  This covers writing ( or generating) the policy, tools to assist with the generation and some details about what types of information must be defined by the "business" before they can be placed into a formalized privacy policy.