This document is an eBook that serves as a comprehensive guide for selecting an MQTT Broker for IoT service providers. It begins by outlining the critical role of the MQTT Broker in facilitating messaging between IoT devices, emphasizing that the selection process is the initial and crucial step in any IoT project. The eBook presents various factors to consider when choosing an MQTT Broker, including security, clustering, auto-scaling, and data integration capabilities. It also includes a detailed examination of popular open-source MQTT brokers, discussing their advantages and disadvantages. A side-by-side comparison is provided to assist readers in determining the most suitable broker for their specific project requirements. The document aims to empower readers with the knowledge necessary to make informed decisions regarding MQTT Broker selection, ensuring alignment with their unique needs and project goals.