Paranoia is an instinct or thought process that is believed to be heavily influenced by anxiety, suspicion, or fear, often to the point of delusion and irrationality. Paranoid thinking typically includes persecutory beliefs, or beliefs of conspiracy concerning a perceived threat towards oneself (i.e. "Everyone is out to get me"). Paranoia is distinct from phobias, which also involve irrational fear, but usually no blame.

Making false accusations and the general distrust of other people also frequently accompany paranoia. For example, a paranoid person might believe an incident was intentional when most people would view it as an accident or coincidence. Paranoia is a central symptom of psychosis.