In the fall of 1969, MIT extended an open invitation to all of its undergraduate students to join the professional research activities of the faculty. This undergraduate research program rapidly increased in size, scope, impact, and diversity. In this article we report on the Undergraduate Research Opportunities Program (UROP) in the MIT Physics Department: the philosophy and objectives of the Physics program, its organization, rules, funding, growth, atmosphere, problems, and accomplishments. By the end of its first three years, Physics UROP included more than 50% of all the undergraduates enrolled in physics. Evaluations of UROP by faculty, administrators, and students were uniformly enthusiastic. This article presents the outline of how Physics UROP was established and how it evolved. Now in its seventh year, UROP has survived to maturity without becoming a cumbersome bureaucracy.