Recent literature on the acquisition of "more" and "less" is reviewed with special emphasis on some key issues. The overriding goal of studies in this area has been the discovery of the developmental sequence that the child follows in acquiring "more" and "less," and, more generally, all comparative structures. The earliest empirical studies on this area provided some initial evidence that "less" means "more" for young children. On the basis of these empirical findings, the investigators, along with others, concluded that "less" and "more" are synonyms for children at some immature point in their development. However, contradictory empirical evidence indicated that at least some groups of children do not treat "less" and "more" as synonyms. Because of the discrepancies found between some of the studies in children's responses to "less," investigators became more aware of the possibility that the type of task required of the child may influence the accuracy and type of responses. It is suggested that "less" is never synonymous with "more" for a child. There ls some evidence that the non-linguistic response bias of choosing the greater of two amounts coincides with not knowing "less." Virtually all the studies conclude that children learn "more" before "less." It is concluded that the acquisition of an adult-like understanding of "more" appears to take years of development. (SW)