Guar gum and partially hydrolyzed guar gum (PHGG) are food ingredients that have been available for many years. PHGG is the partially hydrolyzed product from guar gum obtained from the Indian cluster bean (Cyanopsis tetragonolopus). The gum (CAS Registry No. 9000-30-0) is composed of galactomannan, a gel-forming polysaccharide with a molecular weight ranging from 200 to 300 kDa. The intact and partially hydrolyzed forms have multiple food applications. The intact material can be used to control the viscosity, stability, and texture of foods. PHGG is highly soluble and has little physical impact on foods. Both forms are indigestible but are excellent sources of fermentable dietary fiber. The caloric value of intact guar gum is accepted as 2.0, whereas the caloric value of PHGG has not been firmly established. It is the goal of this paper to review the chemistry, safety, in vivo effects, and caloric value of PHGG.