The exact nature of the SCP Foundation are still unknown, but over the years there have been many myths over the years, involving everything from the Angel who guarded the Garden of Eden to a super natural post-Civil war factory. The true origin will likely remain hidden forever, but it was known that Foundation was operating already in the 19th Century and was a powerful organization on the world stage by 20th Century, being acknowledge by both the Anomalous community and most national government.After the World war 1, the Foundation created a special task force known only as the "Insurgency", which would perform more the questionable tasks of the Foundation. This task force would be deployed in 1925. The Foundation took part in the Seventh Occult War( which ran concurrent with the World War 2),and while its role in the war was not known, it is presumed they were fighting the Thule Society and Ahnenerbe Obskurakorp, who tried to perform the "Rite of Solomon".Eventually the war ended, and the Foundation continued to its normal duties of containing. The Global Occult Coalition was formed, since the government of the world wanted a force against the anomalous that they could control, but the Foundation still continue to work with them, In 1948, the Insurgeency actually went A.W.O.L. and rose up against the Foundation, obtaining several with several SCPs in the process, and reanming themselves to the Chaos Insurgency. In the course of the 20th century, the Foundation came across thousand of anomalies, making the best in containing them, as well as coming in contact with rival and enemy faction. In the 1950 to 1980s, the Foundation would also discover to the reemergence of Sarkicism, with devastating anomalies in Europe like SCP-610 and SCP-2191-3, as well cults like Adytum's Wake and the Hunter's Black lodge spreading their influence. The Foundation would also discover several anomalies tied to an ancient, malevolent Eldritch being, for which they would have to perform some of its most questionable procedure. In 2007, the Foundation would discover Anderson Robotics, a corporation that develops advance Androids and artificial intelligence, who used advanced-fly-like-drones to spy on the Foundation. Despite the emergence of these things, the Foundation has been unable to pursuit their mission statement without breaking their status quo too much.

Ranks and Structure
All Foundation personnel are sworn to secrecy and are excepted to be loyal and professional in their duties. For example matters like personal morals or superstition should never cloud their judgement during work.

O5-Council
The SCP Foundation is led by the Overseer council, also know as the O5 council. The O-5 council consist of usually 13 people who are often defined as O5-1 through 13. The O-5 council has unlimited access to all files and reports without any data expunged or redacted. The Council usually decides major decisions with anomalies that have existential threats to humanity or the universe at large but can influence anything. It is often speculated that O5's might be anomalous themselves.

Elite Committee
The elite Committee also weilds lots of power inside the foundation. Most personnel consider the Elite Committee a joke or myth, but in reality, the leaders of this Committee are described to have the same power as the O5 council, if not more. They hide in plain sight and apparently have some authority over the O5 council. The Committee decided what is ethically acceptable for the Foundation to do in their mission statement.

Site-Directors

Site-Directors are high-ranking researchers that lead different containment sites around the world.They often have Assistant Directors of different expertise that assist them inside the facilities. Site-Directors are also usually the highest ranking officials who still have a full name and not a numeric designation like with the O5 council.

Mobile Task Force

Mobile Task Force or 'MTF", are the Foundation's most effective and skilled personnel. They can be anything from the scientist and researchers to Elite Special Force Soldiers(The most common variant used in stories or media about the SCP Universe). Mobile Task Force are, as the name suggests. mobile and can operate on either Containment sites or in the field.They usually deal with the most dangerous anomalies,where the more common field and recovery agents might lack knowledge or training. MTf also have specialties:Example MTF Mu-4(Debugger) is specified in tracking anomalous electronic devices, technology, and transmission, and either try to contain or block them. The most famous /infamous Mobile Task force is MTF Alpha-1(Red-Right-hand), who consist of the Foundation best and loyal operatives and employees.Despite this MTF Alpha-1 is often connected to the creation of the Chaos Insurgency, a rival organization that seeks to destroy the Foundation.

Researchers

Researchers are doctors and scientists that research on the anomalies. Their duties can vary from experiments on the anomalies to developing Special Containment Procedures. Security clearances and also rank very from simple Research Assistants to site-Directors and everything in between.The expertise of researchers can vary from different scientific fields like technology to zoology or different anomalous field. Example for the ladder is Dr. Judith low is specialized with anomalies that relate to Grand Karcist Ion and his following, Sarkicism.

Containment Specialists
The containment Specialists are employees who designed and uphold the Special containment procedure for anomalies. Containment Specialists can be anything from technicians to doctors to security personnel and these duties overlap with over ranks.

Security Personnel 

The facilities of the foundation employs Security Personnel that serve as the primary defense force in doors. Their duties rank from guarding anomalies to serving as body guards for higher rank officials. Their duty often overlap with  Containment Specialist and MTFs.

Field agents

Field agents are responsible for detecting anomalies in outside world. They can be placed in any organization whether it is an government, a company or in a military or law enforcement organization. They serve as eyes and ears and contact the Foundation when something anomalies is detected.

Recovery teams

Recovery teams are usually called in Field agents when an anomaly is found. They are responsible for capturing the anomaly and transporting it back to the Foundation-owned facility. As mentioned before, with more dangerous anomalies MTFs are sent in. 

Class D personnel
Class-D-personnel are the lowest ranking staff at the Foundation. Usually recruited from convicted criminals, especially the death row criminals. They often serve as human-test subjects with anomalies, be it on facilities or in the field. Other groups and civilian organisation see this usually as human-rights-violation, though the Foundation sees this as necessary. In older canon, Class D personnel were automatically terminated after 30 days of employment; in newer canon  they are often given Class B amnestic drugs instead at the discression of security and medical staff. In some cases when the Foundation is running out of D-class and none of death row prisoners are available, the Foundation may enable Protocol 12, which recruits class D personal from other prison population, refugee populations, or in extreme cases civilian sources.  

Other Ranks

The Foundation also employs more mundane staff such as communication specialist, kitchen staff, accounting,archives,janitorial staff and electricians, who do not work directly with anomalies, but are vital in a day-to day operation.  

About SCPS

While literally thousands of SCPs have been contained by the foundation, there are several notable ones that are popularly associated with the Foundation. It should be noted that all of these SCPs are contained by the Foundation and are not affiliated with the Foundation personnel. 

Notable SCPs

SCP-049:An immortal plague doctor who uses a mysterious treatment on human subjects that render them as brain-dead and hostile zombies.

SCP-087:An endless stair case going down that contains a humanoid figure,SCP-087-1. The constant sound of crying can be heard deep within SCP-087.

SCP-096:A tall, pale, humanoid that will kill anyone or anything that sees it face. It is indestructible and unstoppable when enraged.

SCP-106:An elderly humanoid with the ability to pass through any material and create pocket dimensions at any time. 

SCP-173:One of the first SCPs, SCP-173 is a statue-like creature that cannot move when in direct eye sight, but can move unfathomably fast when looked away from. It will kill anything it can by breaking the necks.

SCP-682:An indestructible reptilian monster with a hatred for humanity and a desire for all of it to be wiped out. 

Known Membership

The SCP Foundation employs thousands of people such as researchers, agents, and guards. The work these individuals perform is often morally controversial in nature( such as D-class personal and Procedure 110-Montauk): however, the work is always meant to protect mankind and preserve normality.