The Military Grid Reference System (MGRS) is the standard use by all NATO military forces to locate any point on Earth down to one meter locations. This is called a "geocode" - a unique identifier for any location or object that is short and can be fairly easily read by humans. The MGRS coordinate system is a vital part of land navigation and location coordination during operations. However, information online about the system is not particularly easy to understand. This book is intended to provide both a broad explanation of MGRS, but also deeper detail on elements of MGRS that are not immediately obvious. It also explains some practical uses to assist with land navigation, like calculating distances and azimuths.