The problem of psychologism is a recurring one in Husserls thought and since 1900 it has accompanied its development. With the findings of the phenomenological reduction, around 1906, Husserl recognizes and starts arguing against a new kind of psychologism, namely transcendental psychologism. Starting in the 1920s, Husserl develops the program for a phenomenological psychology. This paper aims at investigating how phenomenological psychology and transcendental psychologism are related