Early ontogeny is still the least well-known part of the molluscan life cycle, despite its unarguable significance in ecology, biogeography, and evolution. The past decade has seen an acceleration in biological research on molluscan embryonic and larval development, and paleontologists have recently begun to explore this field as well. Although the very earliest phases of ontogeny are inaccessible to the paleontologist, a remarkable amount of information can be derived from the preserved details of larval shell morphology. The fossil record thus affords rich opportunities to study directly the development of extinct species, both from a phylogenetic standpoint and for tracing the evolutionary and biogeographic effects of these early stages in life history. Access to long-extinct clades and an ability to document rates and patterns of evolution allow paleontologists to test hypotheses that can be addressed only indirectly using Recent data. Here I will emphasize these paleontological aspects of molluscan development (see also Jablonski and Lutz, 1983); for the more strictly biological aspects of reproduction and embryology, see Giese and Pearse (1977, 1979), Verdonk et al. (1983) and Tompa et al. (1984).