This chapter examines the significance of processes of semiproletarianization for ecological change and the nature of the labor scarcity that affects many contemporary rural communities. It examines its relationship to strategies of economic diversification, seasonal and temporary migration, and the terms of trade faced by rural households. The chapter also examines the major debates over labor availability that has emerged in the work of economists and anthropologists concerned with rural development. It reviews these debates, the lack of congruence between models of labor dynamics and empirical studies is striking, and the role of particular models in justifying specific agricultural or agrarian policies is revealed. The chapter describes the policy dilemmas that arise in attempts to introduce conservation measures when peasants are "part-time" farmers. It draws on the experience of two attempts to introduce improved land management techniques to rural producers—one in Jamaica and the other in Peru.