Paul Meehl, a pioneer of twentieth-century psychology, introduced a generation of psychologists to the philosophy of science. In contrast to many psychologists, he developed a skeptical attitude through early exposure to the philosophical writings of Bertrand Russell and Karl Menninger. His philosophical commitments later in his career were driven by connections to prominent philosophers such as Herbert Feigl, Karl Popper, and Imre Lakatos. An attempt to summarize the full extent of Meehl’s contributions to psychology could fill an encyclopedia on its own. In this entry, we try to capture the breadth and scope of Meehl’s extensive scholarship and contributions to theoretical and philosophical psychology. These include his works on (1) construct validity theory, (2) philosophy of science and theory-building within psychology, (3) critiques of null hypothesis statistical testing, (4) clinical judgment versus statistical prediction, (5) the Minnesota Multiphasic Personality Inventory, and (6) theory and application of taxometric procedures. A notable throughline of these different areas of Meehl’s scholarship is his advocacy for the importance of the philosophy of science and theory-building within psychology.