The field of sexual differentiation and gender-related behavior has become, over the last 30 years, one of the most vigorous areas of study in developmental psychobi ology. Besides having intrinsic interest for most of us, the field provides an ideal context in which to explore the complex interrelations between genes and hormones; hor mones and neurochemistry; neuron survival, growth and connectivity in different chemical and sensory environ ments; and the development and expression of behavior patterns as a function of hormonal and species-typical physical and social environments. This issue of Psychobiology was not intended to pro vide a comprehensive review of the major areas of research in the field. A number of recent publications serve this function admirably (see, for example, Adler, Pfaff, & Goy, 1985; Crews, 1987, reviewed this issue; Reinisch, Rosenblum, & Sanders, 1987, reviewed this is sue; Yahr, 1988). Rather, the papers published here serve as examples of ongoing research, representing the varied concerns of scientists within the field. While reading these papers and others recently published, I have been im pressed by the recurrence of several themes and theoreti cal issues that have emerged in recent years from chang ing perspectives in the broader discipline of developmental biology. Changing perspectives often have the capacity to make new findings possible, but more importantly, interpret able, and suddenly obvious. One is reminded, for exam pie, of the better understanding of the significance of the many reports ofbrain hemispheric asymmetries in numer ous vertebrate species (see Glick, 1985; Kolb, Sutherland, Nonneman, & Whishaw, 1982; Nordeen & Yahr, 1982) that came with the recognition that many parts of the body, including the brain, show maturational asymmetries in growth (Corballis & Morgan, 1978). Tbe realization that cell death is anormal process in the development of the nervous system and that survival depends on the chemi cal environment, on afferent and efferent connections, and on neuronal activity not only has transformed thinking