The individual contemplating research on play faces a classic approach-avoidance conflict. Few areas in the biological and social sciences have witnessed a more spectacular "growth" in the past 15 years than play. Play unites and cuts across disciplines leading very directly to questions relating to species adaptation and developmental change. Yet play is also a minefield for the unwary, harboring a huge array of conflicting definitions, theories, and perspectives. The essence of play is paradox. This paradox both invites inquiry and repulses scientific systematization.