Alfalfa is America's most important perennial forage crop. It is usually harvested several times a year and fed as hay, silage, greenchop, pellets, or cubes. Alfalfa may also be used for pasture or grown for seed production. It is high yielding and a good source of available protein for livestock. It can be grown alone or in combination with grasses and other legumes. In crop rotations, alfalfa improves soil structure, builds soil fertility, and reduces pest problems for other crops. Proper management throughout the life of an alfalfa stand is essential because conditions in one season affect production in following years. Proper management involves several steps: • Selecting the best variety with pest resistance appropriate for the local environment. • Proper liming and fertilization (and, in some states, irrigation). • Timing of cultural practices (such as pest control) for maximum benefit. • Scheduling harvests to maintain the health and vigor of the stand. The result of good management is a balance between productivity, quality, and stand persistence. Although a great deal is known about alfalfa management, production practices must be refined continually to maintain the competitiveness and profitability of enterprises that use alfalfa. All aspects of management are built around the growth and development of the crop. A better understanding of growth and development is the key to better management. Today, the major limitation of alfalfa management in the humid eastern regions of North America is inadequate control of the nutritional quality of the feed. We have been studying ways to predict the quality of growing alfalfa as a step for improving management. It has long been known that the quality of alfalfa decreases as the crop matures, but the prediction of quality from stage of maturity has awaited precise definition of the mean stage of development. The concept of mean stage should be useful to everyone who works with alfalfa. This publication briefly reviews the concepts of forage quality and presents detailed descriptions of the stages of alfalfa development. Two methods for calculating mean stage of development are described and related to management and forage quality. The information is intended for use in research, teaching, and extension. Photographs and quality parameters were taken from a two-year-old stand of 'Honeoye' alfalfa grown near Ithaca, New York. Commercial stands from throughout the United States have also been studied.