Commonly referred to as the DPA, the Department of Paranormal Activities is the base of operations for Nathan Dawkins, Cole Freeman, and, initially, Jodie Holmes. It is the sole driving force throughout the game.
Its origins are not described. It appears to primarily focus on the study of the Infraworld and its denizens, though given its title, it likely investigates other paranormal phenomena as well. During the chapter First Interview players can look around Nathan's office and interact with various things, one of which is an experiment that Nathan did prior to meeting Jodie. He explains that they were recording a table over a period of time and noticed it moved 13cm from its original position.
There is also various papers stuck to boards around the office that show various other types of investigations and news articles about ghosts and paranormal activity, one can be seen behind Nathan on a board about the "White Lady".
Nathan and Cole are both members of the DPA, who worked with Jodie when she was younger. After Jodie leaves the custody of the DPA, and is recruited by the CIA, Nathan evidently continues his research while Freeman conducts his own research into the nature of the various Infraworld Entities in an attempt to identify and classify races. Nathan is eventually promoted to Executive Researcher, and heads the Infraworld project with government funding.
The DPA appears to liaise closely with the U.S. military in addition to the CIA. Although, it is likely the military and CIA utilize the DPA's research and technology for their ends versus the DPA pulling the strings. It is not entirely clear if the security personnel deployed in the chapter The Condenser are DPA specific, or otherwise units assigned from the CIA or military.