Yale's residential college system, now more than 70 years old, is perhaps the most distinctive feature of the College. The residential colleges allow students to experience the cohesiveness and intimacy of a small school while still enjoying the cultural and scholarly resources of a large university; the residential colleges do much to foster spirit, allegiance, and a sense of community at Yale.
Before freshman year, all incoming undergraduates are assigned to one of Yale's twelve residential colleges. Students remain affiliated with their residential college for all 4 years (and beyond). Yale makes every effort to represent the diversity of the entire undergraduate community within every residential college. In this sense each college is a microcosm of the larger student population. The residential college system offers students a familiar, comfortable living environment, personal interaction with faculty members and administrators, and exciting opportunities for academic and extracurricular exploration.
Every residential college has its own master and dean, both of whom are Yale faculty members. The master and dean live in the college with their families and eat their meals with students in the dining hall.
The master is the chief administrative officer and the presiding faculty presence in each residential college. He or she is responsible for the physical well being and safety of students in the residential college, as well as for fostering and shaping the social, cultural, and educational life and character of the college. During the year, he or she hosts lectures, study breaks (especially during finals), and Master's Teas—intimate gatherings during which students have the opportunity to engage with renowned guests from the academy, government, or popular culture.
The dean serves as the chief academic and personal adviser to students in his or her residential college. Students submit course schedules, drop courses, or convert a course from the Credit/D/Fail option to a letter grade through the residential college dean's office. If a student is having difficulty with a particular course, the college dean can often help by talking with the student's instructor or with the relevant department's director of undergraduate studies, or by referring the student to one of the tutoring programs administered by each residential college. Getting to know all residential college students as individuals helps the dean to address their concerns as personally and effectively as possible.
Excerpt from the Admissions website.