 The Bayley Scales of Infant and Toddler Development–Third Edition (Bayley-III) is a revision of the frequently used and well-known Bayley Scales of Infant Development–Second Edition (BSID-II; Bayley, 1993).Like its prior editions, the Bayley-III is an individually administered instrument designed to measure the developmental functioning of infants and toddlers.Other specific purposes of the Bayley-III are to identify possible developmental delay, inform professionals about specific areas of strength or weakness when planning a comprehensive intervention, and provide a method of monitoring a child’s developmental progress.