Scientists, individually and through their national academies, have often pointed to the major role of population growth in damaging humanity's life-support systems, emphasizing the overriding need for population stabilization. Demography and its practitioners, however, in focusing on technical analyses of population change and its components, have largely neglected these critical issues. Where they have taken an interest in population—environment relationships, their voices have been little heard in public debate and have had scant political impact. Demographers should promote their expertise more aggressively, in particular through a new environmental demography, modeled perhaps on environmental economics. This should be a collaborative enterprise with ecologists and other environmental scientists, concerned with issues of carrying capacity, encouraging and planning for future population reduction, and researching population policies that are humane and accord due attention to environmental sustainability.