Borneo and the eastern side of the Malay Peninsular are considered to be "environmentally critical" areas because of the massive deforestation that has taken place since the 1960s. This publication traces the course of their modern transformation, beginning with a description of the natural environment and its dynamics, reviewing the considerable changes that occurred before the modern period, and examining changes since World War II. A wide range of issues are covered, including possible environmental endangerment in relation to timber-related industries, biodiversity, transmigrants and other settlers and the possible consequences of deforestation for global warming. Conclusions are mixed and indicate that the greatest dangers arise from national policies that continue to treat the region as a "resource frontier" despite the growing resource scarcity.