St. Anselm, 11th century theologian, philosopher, and Doctor of the Church, coined the phrase "fides quaerens intellectum" (faith seeking understanding). This is precisely what theology is: faith seeking understanding. As such, faith is the starting point of theology, which works from the top down (from principles revealed by God and held by faith), while philosophy works from the bottom up (from first principles grasped by the natural light of reason). After being introduced to philosophy, students often look for a concise account of the fundamental principles of Catholic theology. This book is a response to that search.