This chapter considers these matters in depth, including various types of validity and validity evidence, sources of validity evidence, and integration of validity evidence across different sources to support a validity argument for the test. A test must produce reliable test scores to produce valid interpretations, but even highly reliable tests may produce invalid interpretations. Validity is threatened when the test does not measure important aspects of the construct of interest, or when the test measures characteristics, content, or skills that are unrelated to the test construct. For any given test, the term validity refers to evidence that supports interpretation of test results as reflecting the psychological construct(s) the test was designed to measure. Validity is a fundamental psychometric property of psychological tests.