"We own the Calculus." This was a sentiment proclaimed by students who took calculus at the University of Texas as it was taught by Professor R. L. Moore. This book captures the method which facilitates the teaching of students through Inquiry-Based Learning (IBL). It is based on notes taken by the author as a student of Dr. Moore at the University of Texas, Austin, in 1955. It includes Dr. Moore's collection of seminal "problems that teach" -- designed to stimulate creativity and encourage student presentations of their solutions in the classroom. The intention of IBL is to minimize or even eliminate lectures by the instructor and to maximize student participation in the learning process. In the classes taught this way, the students take charge and compete to show their classmates how they solved the problems. The great American mathematician Paul Halmos, says: "The only way to learn mathematics is to do mathematics. That tenet is the foundation of the do-it-yourself, Socratic or Texas Method." Through the last five or so decades, it has evolved into what is now known as IBL and is being promoted, not only at Texas but through regular classes, summer projects, and workshops at several U. S. Colleges and universities, such as California Polytechnic at San Luis Obispo, University of Nebraska, U.S. Naval Academy, University of Chicago, and other places.