They're shrouded in superstition, cloaked in mystery, and are the stuff of legends: Yale's Secret Societies.

Skull and Bones, the most famous, hulks over High Street in the heart of Yale's New Haven campus. But in spite of the prominent placement of its "tomb," few Yalies know what goes on inside. Bones' list of famous members spans every industry in America -- presidents, politicians, corporate titans. None will speak of its mysteries.

But based on interviews with professors, alumni, and some secret sources, we take you inside the tombs, unlocking the legends and lore of Yale's secret societies. (Thanks as well to Alexandra Robbins' "Secrets of the Tomb.")

Made up of about 15 seniors each, Yale's dozen or so secret societies meet every Thursday and Sunday for meals and meetings. Some are more social; others are focused on service or academics. The recruitment process culminates on Tap Night -- an April evening when the campus comes alive with cloaked and costumed students who go from dorm to dorm searching for the juniors they've elected. The taps are then whisked away blindfolded for initiation ceremonies, some to far-off locations, others to elegant restaurants. Oaths are taken. All swear to guard their society's secrets.

Over the years, several of Yale's secret societies have come and gone. Run by alumni trusts, some have run out of money and folded. Other new societies have been created to include those shunned by the likes of Skull and Bones. Here we list the majors -- along with some of the secrets their members have guarded along the way.