Although the great majority of carburizing is still carried out at atmospheric pressure, recent developments in vacuum furnaces and steel technology have meant that carburizing can now be carried out in a more environmentally friendly way under low pressure. The range of material types being carburized under vacuum is increasing with a strongly upward trend towards vacuum carburizing evident in many areas. In choosing a suitable carburizing process, three main choices have to be made: which carburizing technique and gas (or gases) to employ; which type of vacuum pump system to install; and which quenching gas to use. In particular, the selection of carburizing gas has a significant impact on the efficiency and cleanliness of the process, and on deciding the most appropriate vacuum pump system. This paper describes the current state of the art and practical experiences with low-pressure carburizing techniques and examines the various options within these three essential choices. It also considers the safety and environmental implications of these choices.