Welfare assessment requires a wide range of measures as there are many ways in which individuals cope with the environment in which they live. Welfare can be good or poor so the measures of behavior, physiology, brain function, immune system function, injury etc. must provide information about positive and negative states. Measures of feelings and of health are of particular importance. Behaviors such as stereotypies, low or abnormal responsiveness, and excessive aggression are direct indicators of poor welfare. They are especially important when the welfare problems are of long duration. In addition, the behavior of animals is also needed to interpret other welfare measures such as adrenal cortex activity and some aspects of brain function. Glucocorticoids and heart-rate are useful indicators of short-term welfare problems. Acute phase proteins, immune system measures and pathology indicators provide information about welfare in the longer term. In most scientific studies of animal welfare, a combination of behavioral and other measures is needed. The strengths of preferences of animals, for or against resources or environmental impacts give information about needs. They are best indicated, using the methodology of microeconomics, by indices of demand, such as the consumer surplus, that are assessed using behavioral experimental studies.