The importance of water conservation for agriculture has been recognized for centuries. It is now becoming increasingly important because water supplies often are limited, competition for water occurs among different users under many conditions, and food needed for the world population is increasing. We review progress in the understanding of water conservation through the past 100 years and identify some challenges and opportunities for future water conservation efforts. Early emphasis was on plowing to ‘open the soil’ to receive the water. Plowing also was needed for controlling weeds. Early research showed the importance of surface protection to achieve favorable water capture and to reduce soil water evaporation, but suitable practices for use under field conditions were not available at that time. Through the years, many practices were developed and evaluated to improve water capture, reduce evaporation, and increase water use efficiency under rainfed and irrigated conditions, and some remain applicable under some conditions. Stubble mulch tillage, which retains crop residues on the soil surface for erosion control, was first used in the 1930s. It also improved water conservation. With the development of herbicides, production with reduced tillage and eventually without tillage (no-tillage) became possible. Retaining adequate crop residues on the soil surface increases water capture, reduces soil water evaporation, and increases water use efficiency. Unfortunately, no-tillage is not suitable under some conditions and, thus, remains a major challenge to increase its applicability. Other challenges and opportunities for improving water conservation include developing techniques for reducing residue decomposition, identifying or selecting more water efficient crops or crop cultivars, determining crop responses to increasing atmospheric carbon dioxide levels, dealing with herbicide-resistant weeds, bioengineering to develop improved herbicide-tolerant crops, and evaluating water use related to ethanol production.