Phase change material (PCM)-based composite heat sinks have attracted great interest in recent decades, especially in the context of thermal management of portable electronic devices such as mobile phones, digital cameras, personal digital assistants, and notebooks. In this monograph, a detailed analysis of plate fin heat sinks and plate fin heat sink matrix is presented, based on in-house experiments. Performance benchmarks are articulated and presented for these heat sinks. The state of the art in the development of PCM-based heat sinks and the challenges are outlined, and directions on future development are provided. It is our sincere hope and trust that this book will not only be informative but also awaken curiosity and inspire thermal management solution seekers to delve deep into the ocean of research in PCM-based heat sinks and discover their own pearls and diamonds.