A discussion of the Boserup hypothesis, which suggests that higher population and market access leads to improvements in natural resources, is followed by an illustration of the dependence of the Boserup effects on the policy environment that governs the investment incentives of farmers using recent studies of the Machakos district in Kenya and soil degradation in Ethiopia. Growth, the use of land and labour, and the degradation of marginal natural resources in Colombian agriculture are examined. The use of land and labour in Colombia is shown to be driven in highly inefficient directions by a variety of agricultural, land and rural finance policies and programmes which have prematurely and significantly reduced employment opportunities in the sector and have concentrated poverty in rural areas. Labour policies have not contributed in a major way to these adverse trends: the misallocation of land and labour and an exceptionally high female unemployment rate in rural Colombia are consequences of the same policy factors. Policy options for correcting the misallocation of resources, reducing poverty, and relieving the pressure of unsustainable farming on hills and in tropical forest areas with marginal land resources are explored [CAB Abstracts, 1998].