In June 2008 the Congregation for Catholic Education released an instruction on the use of psychology within seminary formation. This instruction provides guidance and insight into the appropriate use of psychology with candidates for sacred orders. It addresses many issues and questions that have arisen regarding the licit use of psychology over the past century. This author examines the historical developments within canonical jurisprudence, moral theology, and the field of psychology that led to this instruction. He then uses these historical developments to understand the issues and topics addressed by the Congregation for Catholic Education as they relate to the praxis of the Church in the United States and how it should be applied within seminary formation.