In the debt-ridden, high-population-growth, resource-mining states of the Congo Basin, conservation of biodiversity is seldom the primary concern of national policy makers or of local resource users. Moreover, the recurring costs of managing protected areas and the opportunity costs of forgoing logging and farming to maintain protected areas are a substantial net drain on national and local economies. Consequently, it is becoming increasingly important that protected areas generate, from user fees or donor contributions, sufficient funds to offset the costs of maintaining them. Government and donor investment currently meet less than 30 per cent of the estimated recurring costs required to manage the protected-area network within central African countries effectively, and cover none of the growing opportunity costs. Nature tourism, the fastest growing sector of the $US3 trillion (3 million million) a year global tourism industry, may offer a source of revenue to help fill this gap in funds. Congo Basin national parks and reserves harbour many charismatic animals (okapi, lowland gorilla, mandrills, bongo, forest elephant) that are likely to attract tourists, and as a result many protected- area managers are sinking capital into the development of tourist infrastructure. This paper reviews the evidence for ecotourism's capacity to generate revenue for protected-area management and appraises the financial viability of nature tourism in the Congo Basin.