A clandestine cell system is a method for organizing a group of people, such as resistance fighters, spies, mercenaries, organized crime members, or terrorists, to make it harder for police, military or other hostile groups to catch them. In a cell structure, each cell consists of a relatively small number of people, who know little to no information concerning organization assets (such as member identities) beyond their cell. This limits the harm that can be done to the organization as a whole by any individual cell member defecting, being a mole, being surveilled, or giving up information after being apprehended and interrogated.
The structure of a clandestine cell system can range from a strict hierarchy to an extremely distributed organization, depending on the group's ideology, its operational area, the communications technologies available, and the nature of the mission. Criminal organizations, undercover operations, and unconventional warfare units led by special forces may also use this sort of organizational structure.