Massive investments in irrigation coupled with the introduction of seed-fertilizer technology brought Sri Lanka to near self-sufficiency in rice by the mid-1980's. Of late, however, policymakers in the government and in donor agencies appear to be shifting emphasis from new irrigation construction to irrigation system rehabilitation and further, to irrigation system management improvement. Despite the critical importance of irrigation investments in the development of Sri Lanka's economy, few attempts have been made to document the investments made in the past in an integrated manner and to demonstrate changes in relative economic profitability among investment alternatives in the sector. The purpose of this paper is to fill this gap by compiling aggregate time-series data on different types of irrigation investment in Sri Lanka during the last four decades and by analyzing changes in the process of irrigation development. First, the process of rapid increase in rice production is documented and the role of irrigation development in this process is identified. Next, past trends in irrigation investments are examined by type of investment, and determinants of the investment trends are assessed. In the succeeding sections, trends in the economic profitability of different types of irrigation investments are analyzed. Implications of the study findings are discussed. (Author abstract, modified)