This introductory chapter explains the coverage of this book, which is about the relation between the concepts of rationalism, Platonism, and God. This book is intended as a contribution to the exploration and exposition of the common ground of the great early modern rationalist theories. It examines contemplation and control in Cartesian philosophy and analyses the priority of the perfect in the philosophical theology of the continental rationalists. It also provides commentaries on the relevant theories of philosophers Rene Descartes, Baruch Spinoza, and Gottfried Leibniz.