Human body composition is an expression of genetic and nutritional factors. It can change as a consequence of exogenous influences such as training, disease, or diet and is therefore of particular interest to nutrition professionals. Two of the main methods of estimating body composition in this review (hydrodensitometry and anthropometry) have been in use for decades, but the third method (bioelectrical impedance) is more recent. The procedure, theoretical basis, assumptions, standard error of estimates, and comparisons with other techniques are presented for each of the three methods. References to general and specific populations are presented that illustrate regression equations for different ages, ethnic groups, and gender. The advantages and disadvantages of the three methods are reviewed with reference made to the alternative compartment models. Other methods (DEXA, infrared interactance) are briefly reviewed.