This document is designed to give a comprehensive technical overview into what steam is in all its forms, how to measure it, where and why it is used for in industrial processes, and to give an insight into unexpected and potentially hazardous situations that may arise from the process configuration and conditions. It uses clear and relatively easy to follow examples, with the minimum of mathematics. However, it does assume a level of interest and curiosity in steam production, distribution and its use, that will be rewarded by taking on-board the principles and practice given in the document.