Accumulating evidence indicates that members of the TRP channel family are components of store-operated Ca2+ channels (SOCs). Agonist stimulation activates SOCs and TRP channels directly and induces translocation of channels in intracellular vesicles to the plasma membrane (PM). The mechanism of TRP channel translocation in response to store depletion and agonist stimulation is not known. Here we use TRPC3 as a model system to show that IP3 and the scaffold Homer 1 (H1) regulate the rate of translocation and retrieval of TRPC3 from the PM. In resting cells TRPC3 exists in TRPC3-H1b/c-IP3Rs complexes that are located in part at the PM/ER interface and in part in intracellular vesicles. Binding of IP3 to the IP3Rs dissociates the interaction between IP3Rs and H1, but not between H1 and TRPC3. TIRF microscopy and biotinylation assays show robust receptor- and store- dependent translocation of TRPC3 to the PM, and its retrieval upon termination of cell stimulation. The translocation requires store depletion and is prevented by inhibition of the IP3Rs. In HEK293, dissociating H1b/c-IP3Rs with H1a results in TRPC3 translocation to the PM where it is spontaneously active. The TRPC3-H1b/c-IP3Rs complex is reconstituted by infusing recombinant cross linking H1c into these cells. Reconstitution is inhibited by IP3. Deletion of H1 in mice markedly reduces the rates of receptor- and store-stimulated translocation, and antagonist-mediated retrieval of TRPC3 present in intracellular organelles. Conversely, infusion of H1c into H1-/- cells eliminates spontaneous channel activity and increases the rate of channel activation by agonist stimulation. The effects of H1c are inhibited by IP3. These findings together with our earlier studies demonstrating gating of TRPC3 by IP3Rs are used to develop a molecular mechanism in which assembly of the TRPC3-H1b/c-IP3Rs complexes by H1b/c mediate both the translocation of TRPC3 to the PM and gating of TRPC3 by IP3Rs.