Gender differentiation is proposed as a model for understanding aspects of gender development. The differentiation process is hypothesized to be patterned in ways similar to those of other major developmental differentiations (e.g. self-other, subjective and objective reality, intention and physical causality): an initial narcissistic, undifferentiated period; recognition of limits with response of protest, sense of loss, denial, etc; a recategorization of experience in which one differentiation product is integrated as part of self, the other recognized to be independent of self, the two in productive relationship. Freud's major observations of feminine development are explored in differentiation terms: the period prior to awareness of sex difference; the recognition of sex difference; further developments in femininity. The differential implications of Freud's interpretation of these observations and of the one proposed are examined.