The use of inertial sensors in sporting and other applications where human locomotion is concerned has grown steadily ever since a spring loaded weight was attached to the body segments to determine its movement characteristics. This monograph has been developed to address these barriers by providing a practical introduction to the technologies, a practical guide to its usage together with case studies to aid in its deployment in applications of interest to the reader. This is presented against a background of its development and likely trends going forward. Like any technology, this work will likely show signs of age eventually, but should prove a helpful companion for the wearable sensor whether they be from an engineering discipline or the sports sciences. Onward!!!.