Compositions and methods relating to regulatable chimeric antigen receptors (RCARs), where the intracellular signaling or proliferation of the RCAR can be controlled to optimize the use of an RCAR-expressing cell to provide an immune response, are provided. For example, a RCAR can comprise a dimerization switch that, upon the presence of a dimerization molecule, can couple an intracellular signaling domain to an extracellular recognition element, e.g., an antigen binding domain, an inhibitory counter ligand binding domain, or costimulatory ECD domain. An RCAR can be engineered to include an appropriate antigen binding domain that is specific to a desired antigen target and used in the treatment of a disease.