It has already been five years since I published my WordPress Plugin Development Cookbook with Packt Publishing. In these five years, WordPress kept evolving and it was time to go back and update all content to current versions and add new recipes to talk about new features introduced to the platform. The result is the Second Edition of the WordPress Plugin Development Cookbook, which you can order online from one of the following sources:
WordPress Plugin Development Cookbook, Second Edition
Yannick's Corner 