In 1999, total rice production in Laos was more than 2.1 million tonnes, enough to make the nation self-sufficient in rice. Over the past 2 decades, total production has increased by about 100%, with most of the increase occurring in the rainfed lowlands where production jumped from 705 000 t in 1980 to 1 502 000 t in 1999. Even though the dry-season irrigated environment has increased production by almost nine times in the past decade (from 41 000 t in 1990 to 354 000 tin 1999) and further small-scale irrigation schemes are planned to achieve a total dry-season irrigated area of about 180 000 ha by 2005, the wet-season lowland environment will remain the most important rice-producing environment for the foreseeable future. Higher yields and reduced year-to-year variability in production can be expected with further intensification of production systems in the lowlands. However, further improvements in production will depend on higher levels of inputs and continued alleviation of some production constraints. The uplands will become less important for rice production as alternative, more sustainable technologies are developed to replace the current ‘slash-and-burn’ and shifting cultivation practices. This paper summarizes the known main abiotic and biotic production constraints in each of Laos’s rice-producing environments: wet-season lowlands, dry-season irrigated, and rainfed uplands, but not those socioeconomic constraints that can also have significant impact on farmer attitudes and production. The major production constraints in the main rice-producing environment—the wet-season lowland ecosystem of the Mekong River Valley—are drought and poor soil fertility. However, more than 10% of the wetseason lowlands in the central and southern agricultural regions are also regularly affected by flooding of the Mekong River. In these areas, flood damage is often regarded as a greater production constraint than drought. In the dry-season irrigated environment, poor soil fertility is the main abiotic constraint. Insect pests are becoming increasingly important in both these production systems. In existing production systems in the rainfed uplands, the main constraints are, in decreasing order of significance, weeds, rodents and drought. Farmers’ perceptions of the relative importance of production constraints in the uplands are generally more accurate than those in the lowlands. Poor soil fertility is often not rated among the most important constraints in the wet-season lowlands and dry-season irrigated environments, despite experimental evidence that often the greatest yield increases can come from improved plant nutrition. Until recently, farmers’ perceptions of the importance of insect pests in the lowlands often exaggerated their economic significance.