This document discusses using APC and Memcached to improve PHP performance. It summarizes APC as an opcode cache that caches compiled PHP scripts to reduce parsing and compilation overhead. Memcached is described as a distributed memory caching system that stores objects in memory for fast retrieval to offload processing from databases. Examples are given of how APC and Memcached can each speed up a PHP application and improve concurrency. Installation and usage of both is briefly outlined.