It’s no mystery that America's colleges and universities are home to some of the most exclusive secret societies around. While some are more mysterious than others, all manage to remain relatively hush-hush. The nature of these clubs has led to all manner of speculation, from pop-culture spoofs to conspiracy theories involving some of the highest-ranking government agencies, about what goes on within their ranks.

Here’s a look at what little we know, or don’t know, about 10 of the most infamous of these underground societies. But shhhhh… It’s a secret!

1. Skull and Bones

Institution: Yale University

Founded: 1832

Notable Members: William Howard Taft, George H.W. Bush, George W. Bush, John Kerry, David McCullough

Interesting Facts: Skull and Bones could be considered Yale’s best-kept, worst-kept secret — while everyone knows about it, no one really knows about it. Only those who are tapped are truly aware of what goes on in “The Tomb,” the group's windowless HQ. It's been a hot topic of pop-culture speculation and several books, including Alexandra Robbins’ The Secrets of the Tomb: Skull and Bones, The Ivy League and the Hidden Paths to Power.

Infamous Incidents: Depending on who you talk to, Skull and Bones was allegedly involved in the creation of the nuclear bomb and the assassination of President John F. Kennedy. In addition, rumors have circulated that it was created by the CIA to form a pipeline of employees from Yale. It is also believed that members of Skull and Bones stole the skull of Geronimo, who was buried on the grounds of Fort Sill, OK, where he had been a prisoner of war for 20 years. While several members of the society, including Prescott Bush, were stationed there, they allegedly dug up the skull and brought it back to The Tomb.However, it is very likely that these stories are little more than legend.

2. The Flat Hat Club

Institution: College of William & Mary

Founded: 1750, revived in 1916 and 1972

Notable Members: Thomas Jefferson

Interesting Facts: The Flat Hat Club got its name from what are now known as graduation caps, the society's trademark hat. However, the original initials, F.H.C., are actually thought to stand for Fraternitas Humanitas Cognitioque —​ Latin for Brotherhood, Humaneness, and Knowledge. The F.H.C. Society is the oldest-known secret society in the U.S., initially founded in 1750. The club disbanded during both the American Revolution and World War II, presumably due to the lack of males attending college.

Infamous Incidents: The Flat Hat Club, whose members only identify themselves as an organization and never as individuals, often donates money to the school to be used to better student life in some way. Once, Samuel Sadler, a former vice president for student affairs, said an email popped up in his inbox saying that the Flat Hat Club would like to provide textbooks for students in need.

3. Quill and Dagger

Institution: Cornell University

Founded: 1893

Notable Members: E. B. White, Marc Lacey, Oswald C. Brewster, Paul Wolfowitz

Interesting Facts: Quill and Dagger was the first of the Ivy League societies to admit women into its ranks. With membership now being too difficult to conceal, the names of newly tapped Quill and Dagger members, like those of several other secret societies at other campuses, are published in Cornell's student newspaper. Quill and Dagger, however, takes this one step further and publishes a book, available on Amazon, with the names and addresses for each member. This society has also embraced social media and operates a LinkedIn group for alumni.

Infamous Incidents: In the early '90s, Quill and Dagger was accused of “blackballing” activist minorities who were against "the establishment." Minorities, who otherwise would have been on the short list for getting tapped, weren’t admitted if they took part in any activist movements that current members and alumni saw as anti-establishment. However, at the time of this accusation, 12 of the 40 members of Quill and Dagger were minorities.

4. Cadaver Society

Institution: Washington and Lee University

Founded: 1957

Notable Members: Unknown

Interesting Facts: The Cadaver Society is thought to be comprised of mostly pre-med students, but no one really knows since membership is still successfully kept in the dark. Meetings only occur after dark, with members dressed in black capes with hoods to conceal their faces. The meeting place is unknown, but it has been speculated that there is a system of underground passageways used by the members to keep themselves invisible from the rest of campus. Many theories exist regarding the entrances to these passageways, including suspicious doors that are always locked in the science building's basement, manhole covers, and a small door in the wall of the Leyburn Library. Its symbol — a skull inside of a ‘C’ — can be seen across campus and is most often left at the scene of various pranks.

Infamous Incidents: Before big games, the Cadaver Society’s symbol could traditionally be found painted on the football field. Since the installation of a turf field, it can be seen on the adjacent hillside.

5. Seven Society

Institution: University of Virginia

Founded: 1905 (rumored)

Notable Members: John Lloyd Newcomb, Joseph W. Twinam, Edward Stettinius Jr.

Interesting Facts: The Seven Society was formed when eight students agreed to meet for a card game and only seven showed up. This society is so secretive that members are only revealed after they have passed away, via a wreath of black magnolias in the shape of a seven placed upon the grave of the deceased. In addition, the university chapel bell reportedly tolls in a dissonant seventh chord, seven times, in seven-second increments, on the seventh of the hour. Should you wish to contact the Seven Society, the only way to do so is to place a note at the base of the Thomas Jefferson statue in the University Rotunda.

Infamous Incidents: In 1947, the commencement address was interrupted when a small explosion occurred in front of the stage. After the smoke cleared, a check for $177,777.77 was found floating to the ground. This money was used to create an interest-free loan for any student or faculty member in financial trouble.

6. Eucleian Society

Institution: New York University

Founded: 1832

Notable Members: John Harvey Kellogg, Walter Reed, Frederic Tuten

Interesting Facts: NYU's Eucleian Society, while exceptionally secret today, wasn’t always so. The society initially served as a literary and debate group for students that often hosted lectures that were open to the public.One of the most notable lecturers? Edgar Allen Poe, who became such a popular guest among the group that they nicknamed themselves "The Raven Society" after Poe’s most famous poem. Now, little is known about who the members are and what they do, as the society’s records have been redacted or written in a symbolic shorthand understood only by members.

Infamous Incidents: In 2009, the Eucleian Society set off beepers in classrooms across campus with the intention of disrupting class to deliver this message: “Fellow Classmates, Truth is something you find outside of the classroom, outside of the walls of this university, and only from the professor in front of you insofar as he can serve as an experienced guide. We’re not here to preach. We’re here to simply say, NYU has its secrets too. This is your friendly wake-up call. Regards, The Eucleian Society”

7. Order of Gimghoul

Institution: University of North Carolina, Chapel Hill

Founded: 1889

Notable Members: Unknown

Interesting Facts: The Order of Gimghoul is headquartered in an on-campus castle rumored to be constructed on the spot of Peter Dromgoole’s disappearance in 1833. Legend has it that Dromgoole entered a duel over a girl he fancied and lost, his blood forever staining a rock that now resides next to the castle’s entrance. Originally called the Order of Dromgoole, the name was changed to Gimghoul because it sounded creepier and more sinister. The society operates around the legendary values of chivalry and Arthurian life. To this day, little is known about who the members are, how they are chosen, and what they actually do.

Infamous Incidents: The Chris Gethard Show, a public access show out of New York, made several allegations against the members of the Order of Gimghoul regarding rape in recent years. The show even went as far as going to the campus to demand that someone speak to them. However, all of these allegations have remained unfounded.

8. Wolf’s Head

Institution: Yale University

Founded: 1883

Notable Members: William Wrigley Jr., Charles Edward Ives, Rogers Morton

Interesting Facts: Rounding out Yale’s “big three” along with Scroll and Key, Wolf’s Head was created by a number of junior males rejected from Skull and Bones or the aforementioned. Wolf’s Head was the last all-male society at Yale, finally tapping women in 1992. The society's “tomb,” dubbed "The Hall," is the largest of the university's secret societies. It is rumored that the water bill is higher than all of the First Ward of New Haven put together due to the building’s Olympic-sized swimming pool.

Infamous Incidents: Jessica Alba’s husband, Cash Warren, is an alumnus of Wolf’s Head and, conceivably breaking many of the society’s existing rules, he once brought the starlet to a meeting. Perhaps the members forgot about the concept of secrecy all at once and just couldn’t help themselves, or maybe they wanted to gain a little publicity, but pictures from Alba’s visit were leaked, disclosing the members and giving the public a glimpse of The Hall.

9. The Stewards

Institution: Georgetown University

Founded: 1903 (rumored)

Notable Members: Manny Miranda

Interesting Facts: The Society of Stewards was founded by a group of men who were concerned that Georgetown was losing sight of the Jesuit principles on which it was founded. In 1988, the society, which had until then remained a secret, was exposed by the student newspaper, causing an uproar throughout the campus. The Stewards then went through an internal upheaval, resulting in a split. The original Society of Stewards eventually died out in the 1990s. However, the Second Society of Stewards, which broke off from the original group, is still active today.

Infamous Incidents: The Stewards' reputation — they supposedly use their money and status to push a right-wing agenda — recently cost member Jack Appelbaum the election for student body president. Appelbaum was the top candidate until a group called the Stewards Throat leaked that Appelbaum was a Steward. His campaign immediately took a turn for the worse and he narrowly lost.

10. Order of the Bull’s Blood

Institution: Rutgers University

Founded: 1834

Notable Members: Garret A. Hobart, Louis Freeh, Milton Friedman

Interesting Facts: The Order of the Bull’s Blood is so secretive that many don’t believe it actually exists. Others believe that while the society does exist, it has made up its history in order to be more like the societies of the Ivy League. Nevertheless, its presence is best marked through a slew of pranks, all of which have taken place on Princeton University’s campus in an effort to maintain the ancient rivalry that used to exist with Rutgers. One of the Order’s goals is reportedly to reinstate the annual Rutgers-Princeton football game.

Infamous Incidents: It is rumored that the Order of the Bull’s Blood was responsible for stealing a cannon from Princeton University in 1875, an incident that made national news at the time. The two universities have continually butted heads over which school deserves to serve as the cannon’s home. For more on that rivalry, check out the video below.