Cyclodextrins (cyclomaltooligosaccharides, cyclic [1→4]-α-D-glucans, CDs) are produced by the action of cyclodextrin glucanotransferase (CGTase) on either liquefied starch, maltodextrin, or long-chain maltooligosaccharides. Although numerous bacterial sources for the production of the enzyme are known, the CGTase employed in the reactions described in this chapter is derived from cultures of Bacillus macerans and is available commercially. In the absence of compounds capable of forming inclusion compounds (complexes) with CDs, conversion reactions with B. macerans CGTase normally favor the formation of noncyclic products; overall yields of CD are usually in the range of 35–50%. Of the three CDs formed (cyclomaltohexaose [α-CD], cyclomaltoheptaose [β-CD], and cyclomaltooctaose [γ-CD]), γ-CD is favored the least; its yields are generally 4–7%, based on total glucose-unit content of the substrate. The relative proportions of α-CD and β-CD can vary appreciably according to reaction conditions (such as time, temperature, and substrate concentration); however, in most instances, when a near-equilibrium state has been attained, the yield of β-CD is slightly higher than that of α-CD. Where insufficient time is allowed for attainment of this state, the yield of α-CD often exceeds that of β-CD. CGTase from B. macerans initially favors α-CD production; only in later stages of the reaction does the yield of β-CD approximate or exceed that of its α-homolog.