This document provides an overview of Apache ActiveMQ, an open-source messaging server. It discusses ActiveMQ's features such as high performance, high availability, multiple protocols and transports. It also covers tools for benchmarking and performance tuning ActiveMQ brokers, including the ActiveMQ Performance Module, jms-benchmark, JMSTester, JMeter and OS monitoring tools. The document is intended to help understand how to approach performance tuning of ActiveMQ brokers.