Test validity refers to the degree to which the inferences based on test scores are meaningful, useful, and appropriate. Thus, test validity is a characteristic of a test when it is administered to a particular population. This article introduces the modern concepts of validity advanced by S. Messick (1989, 1996, 1996). Traditionally, the means of accumulating validity have been grouped into the categories of content-related, criterion-related, and construct-related evidence of validity. Messick considered the traditional concept of validity to be fragmented and incomplete because it fails to take into account evidence of the value implications of score meaning as a basis for action and the social consequences of score use. Messick identified six aspects of validity that are general validity criteria or standards. These are: (1) content; (2) the substantive aspect; (3) structure; (4) generalizabilty; (5) external factors; and (6) consequential aspects of validity. Two major threats to validity that are worth noting are construct underrepresentation and construct-irrelevant variance. (SLD)