The glass transition of foodstuffs is of particular, importance because it is closely linked to the quality of products. For food industries particularly those concerned with dehydration processes (drying, spray-drying freeze-drying,...) ol low temperature processes (freezing, quick-freezing,...), this parameter is of prime interest. This paper presents an easy to understand approach to the glass transition phenomenon explains its influence according to different food processes, and reviews several methods to determine it experimentally or to estimate its value.