This essay explores implications of current trends in developmental science forunderstanding psychopathology at the dawn of the new millennium. Over the past half century, ithas become clear that uniform and general principles of development (i.e., those that areapplicable at all times, to all people, and in all places) will be of limited utility in understandingthe processes of greatest interest in development and psychopathology. Instead, such processesare characterized by complexly organized individuals engaged in developmental transactionswithin multiple contexts (ranging from the biological environment of neurons to the culturalsystems of meaning that shape people's lives). These transactions in turn often yieldvariable outcomes. In order to portray how we have come to this conclusion, we first provide aview of contemporary research in three areas of early development: the biology of the developingbrain, the complexities of early emotional development, and the cultural contexts of childdevelopment. We then trace how an increasing appreciation of organized complexity,developmental transactions, and the meaning of context have played out in theemerging field of infant mental health before closing with our vision of new opportunities for thestudy of experience in the midst of variation.