Officially founded in 1717 with the opening of the Grand Masonic Lodge in London, the Masons are generally considered to be the longest-lasting secret society that we're aware of. Masons typically conduct their meetings in a highly ritualized fashion, complete with secret handshakes and plenty of references to architectural symbols, such as the square and the compass, and even refer to God as 'The Great Architect of the Universe.'
In order to become a Mason, you typically have to be recommended by one or more current members, who will initiate you as an 'Entered Apprentice.' Once you start gaining more knowledge about Masonic rituals, you may end up moving up the ranks, first becoming a 'Fellow Craft,' and finally a 'Master Mason.' Many religions frown upon Masonic membership, and the Catholic Church states that "faithful who enroll in Masonic associations are in a state of grave sin and may not receive Holy Communion."
On May 1st, 1776, a movement of freethinkers was created in Bavaria, whose followers came to be known as the Illuminati. Even though they weren't allowed to operate legally, and were heavily persecuted, it is said that quite a number of progressive politicians and influential intellectuals joined them over the years. One aspect of this society that appealed to many of the members was the fact that you didn't have to believe in God to become a member, unlike the Freemasons.
This gave atheists and humanists the chance to discuss their ideas more freely and is also the reason why members of the public felt that the Illuminati were out to overthrow organized religion. Due to a mixture of internal struggles and external persecution, the Illuminati officially dissolved in the late 18th Century. However, some conspiracy theorists, such as Was Penre and David Icke believe that the Illuminati are still operating, and are using the governments of the world as puppets, in order to establish a One World Government based on atheist and humanist principles.
Originally known as the Brotherhood of Death, the Order of Skull and Bones originated in Yale University in 1832 and its membership is only open to an elite few. They meet every Thursday and Sunday in a place they call 'The Tomb,' and many of the rituals they conduct resemble ones used by the Freemasons.
Little is known about what they discuss during their meetings, however, a significant number of members have gone on to achieve a great deal of fame and fortune. In fact, both Bush presidents have been proven to have been members of the Skull and Bones (George H. W. Bush can be seen on the left of the clock in the above photo). Like many other secret societies, this one is also surrounded by a whole host of conspiracy theories, the most popular one being that they were actually responsible for creating the CIA.
Founded in the early 1400s by Christian Rosenkreutz, the Rosicrucians have frequently been accused of using occult rites in order to change the world. While they kept quiet for around 200 years, the publication of 3 manifestos in the 1600s suddenly brought them into the limelight. All three of these documents talk about alchemy, chemistry, and secret knowledge.
Modern conspiracy theorists believe that the Rosicrucians have an immensely broad range of influence, and were responsible for founding the Illuminati, the Freemasons, and the Invisible College. There are also some people who believe that the Rosicrucians have been the guiding force behind many revolutions and power struggles across the globe.
In 1954, a group of the world's most influential people met in the Bilderberg Hotel in the Netherlands to plan the following year's political agenda. They continue to meet every year, and while the list of participants as well as their agenda are openly available to the public, they are forbidden to disclose what they actually say and do during these sessions.
The group's official justification for such secrecy is that it allows each member to freely speak their mind without having to worry about getting their words distorted by the mass media. Needless to say, there are quite a lot of conspiracy theories surrounding the Bilderberg Group, and many people are concerned with the influence and reach of these annual meetings.
Way back in the 12th Century, a group of 9 knights swore an oath to protect pilgrims passing through the Holy Land. With time, more and more knights were recruited, and they eventually amassed a considerable amount of fame, wealth, power and influence. There are some claims that they possessed the Holy Grail, the Ark of the Covenant, and the blood of Jesus Christ, however, no compelling evidence has ever backed up these claims.
Unfortunately, most of the Knights Templar ended up tortured and killed, and their society had to be disbanded. However, today there are a number of Templar groups operating once again. Many of them claim to have no direct bloodline to the 12th-century Templars, and only use their rituals and beliefs in their practices. However, there are a few smaller groups who claim to be their direct descendants, yet are unfortunately unable to provide any proof of this.