The importance of forage evaluation for humans and animals; Forages and their role in animal systems; Forage evalation for efficient ruminant livestock production; Intake of forages; Estimating the energy value of forages; Prediction of energy supply in ruminants, with emphasis on forages; Forage evaluation using measurements of energy metabolism; The measurement of forage digestibility in vivo; Faeces as a source of microbial enzymes for estimating digestibility; Enzime techniques for estimating digestibility; The in situ technique for the estimation of forage degradability in ruminants; Cumulative gas-production techniques for forage evaluation; Estimating the protein value of forages; Animal-based techniques for the estimation of protein value of forages; In situ techniques for the estimation of protein degradability and postrumen availability; Enzymatic and microbial-cell preparation techniques for predicting rumen degradation and postruminal availability of protein; Physicochemical approaches; Characterization of forages by chemical analysis; Near-infrared (NIR) spectroscopy: an alternative approach for the estimation of forage quality and voluntary intake; NMR and other physicochemical techniques for forage assessment; Minerals, vitamins, antinutritive and other factors; Trace-mineral status of forages; Major minerals in forages; Vitamins in forages; Secondary plant compounds and forage evaluation; General conclusion and discussion; Current procedures, future requirements and the need for standardization.