This book is an innovative problem-oriented introduction to undergraduate set theory. It is intended to be used in a course in which the students work in groups on projects and present their solutions to the class. Students completing such a course come away with a deeper understanding of the material, as well as a clearer view of what it means to do mathematics. The topics covered include standard undergraduate set theory, as well as some material on nonstandard analysis, large cardinals, and Goodstein's Theorem. AN OUTLINE OF SET THOERY is organized into three parts: the first contains definitions and statements of problems, the second contains suggestions for their solution, and the third contains complete solutions.