Since 1944, the National Research Council has published six editions of Nutrient Requirements of Dairy Cattle. This seventh revised edition, Nutrient Requirements of Dairy Cattle 2001, applies new information and technology to current issues in the field of dairy cattle production. Reflecting the rapidly changing face of dairy cattle production and dairy science, it includes more comprehensive descriptions of management and environmental factors that affect nutrient requirements and provides expanded discussions of nutrient needs for various life stages and levels of production. A revised approach to predicting nutrient requirements increases the user’s responsibility for accurately defining animals, diet, and management conditions to estimate nutrient requirements. A benefit associated with the increased responsibility is the ability of the user to make more-informed decisions in the field. A substantial part of the increase in decision-making power comes from the presentation of requirements with a computer model. Computer models are the only effective means of taking animal variation into account. Unlike static tabular values, computer models such as the one provided in this edition can describe animals in different states with differing needs. A model can accommodate fluctuations caused by the effect of feed ingredients on nutrient absorption and consequently on the animal’s performance potential, which affects its nutrient requirements. The model prepared in this publication was designed to provide practical, situation-specific information in a user-friendly format.