A convenient two-step technique for preparing thin films of the organic-inorganic perovskites (RNH 3 ) 2 (CH 3 NH 3 ) n-1 M n I 3n+1 (R ) butyl, phenethyl; M ) Pb, Sn; n ) 1, 2, ∞) has been achieved. Films of the metal halide, MI 2 , were first deposited onto ash glass or quartz disks using vacuum evaporation or spin-coating. By dipping these inorganic films, at room temperature, into an organic ammonium iodide solution for a short period of time (1-5 min for the layered perovskites), single-phase samples of the corresponding organic-inorganic perovskite thin films were formed. While a variety of solvents can be used for the dipping process, toluene/2-propanol mixtures have been shown to work well for many of the present compounds. The layered organic-inorganic perovskite films exhibited uniform surfaces and strong photoluminescence at wavelengths that were consistent with the corresponding materials made by single-crystal growth from solution. However, dipped organic-inorganic films made from evaporated PbI 2 exhibited a luminescent peak that was red-shifted approximately 10 nm relative to those prepared from spin-coated PbI 2 , perhaps due to states induced near the band edge as a result of crystal defects or surface states. Films of the three-dimensional perovskites CH 3 NH 3 MI 3 (M ) Pb, Sn) were also prepared by dipping MI 2 films into a methylammonium iodide 2-propanol solution. The resulting perovskite films were black, and their X-ray diffraction patterns were in good agreement with those of samples prepared from solid-state reactions or solution chemistry techniques. The present work demonstrates that the new dipping technique can be used as a generic method for synthesizing thin films of a variety of layered and three-dimensional organic-inorganic perovskites. It is expected to be particularly useful for preparing films of organic-inorganic systems in which the organic and inorganic components have incompatible solubility characteristics, or for systems in which the organic component is difficult to evaporate. The structural characterization and photoluminescence results all suggest that the perovskite films prepared using the title method are well-organized, making this method a promising technique to prepare thin films for a variety of potential device applications and scientific studies.