Book excerpt: Earth has limited material and energy resources, while these resources are virtually unlimited in space. It is only a matter of time, before planetary resources are mined and used in-situ to sustain human and robotic exploration or returned to Earth for commercial gain. This book covers a number of aspects related to space resources. In particular, subjects related to mission concepts, exploration approaches, mining and extraction technologies, commercial potential, and regulatory aspects of space resources are covered in detail. This book is therefore a good resource for readers who seek background and deeper understanding of space resources related activities.