This manual for PHP developers focuses on customizing SugarCRM to extend its capabilities. After an overview of the SugarCRM application architecture and its database, it provides a module development tutorial, showing the essential steps for hooking custom modules into the SugarCRM infrastructure, and finishing with common customizations that can be performed against the codebase. Readers need a basic knowledge of SugarCRM as its installation and usage are not covered.SugarCRM is the world's leading commercial open-source customer relationship management software, offering companies of all sizes a more flexible, cost-effective alternative to proprietary applications. Its open-source architecture allows easier customization and integration of customer-facing business processes to build and maintain more profitable relationships. SugarCRM's deployment options include on-demand, on-premise, and appliance-based solutions to suit customers' security, integration, and configuration needs.