Significant technological advances have occurred in the area of polycrystalline thin film photovoltaic technologies based on cadmium telluride (CdTe) and copper indium diselenide (CuInSe@sub 2@, CIS). In the past few years, the many advances made in materials research, device development, manufacturing technology, reliability testing of modules and systems, technical R&D issues relating to CdTe & CIS, and early commercialization efforts underway in the United States and worldwide are reported in this paper. A typical thin-film CdTe solar cell structure is glass/SnO@sub 2@/CdS/CdTe/contacts. A world-record, total-area efficiency of 16.5% has been achieved by scientists at NREL. One of the most active areas of research is the study of the interdiffusion at the CdS/CdTe interface, where diffusion of S in the range of 4%-12% into the CdTe absorber has been observed by SIMS technique. Other areas of research include developing new transparent conductors such as Cd@sub 2@SnO@sub 4@ to replace SnO@sub 2@2, and the study of back contact stability to develop stable thin film CdTe solar cells. A number of vacuum based thin film growth techniques will also be reported. For thin-film CIS-based solar cells, the typical cell structure is ZnO/CdS/CIS/Mo/glass. Low-cost sodalime glass is normally used for device fabrication. In addition, polymer, metal foils, and stainless substrates are being investigated as alternate substrates. The highest world-record, total-area efficiency achieved thus far by NREL scientists for thin-film CIGS solar cell is 21.5% using a concentration of ~14X by the physical vapor deposition method. The CdS is deposited by the chemical bath deposition (CBD) technique. The process is reproducible and quite robust. The Ga:In ratio is typically 30:70. Areas of research worldwide include the role of Na that diffuses from the glass into the CIGS absorber, the optimum amount of Ga which help increase the bandgap from 0.95 eV to 1.2 eV, such that, there is better match with the solar spectrum, and developing alternate buffer layers to replace CBD CdS. The major players developing thin-film CdTe module fabrication are ANTEC Solar, Germany; BP Solar (BPS), USA, First Solar, USA, and Matsushita Battery, Japan. For thin-film CIS technology, the major players are Energy Photovoltaics, USA, Global Solar Energy (GSE), USA, Honda Engineering, Japan, International Solar Electric Technology, USA, Matsushita Industry, Japan, Showa Shell, Japan, Shell Solar Industries (SSI), USA, and Wurth Solar, Germany. Multi-megawatt manufacturing facilities for module fabrication are currently underway in Germany, Japan, and USA. Early commercial products (5-40 W) of CIS are available from SSI, and GSE for military applications. Prototype thin-film CdTe Apollo module with aperture-area efficiency of 11.0% and power output of 92.5 W has been developed by BPS for commercialization in 2003. This work was supported by NREL under Contract no. DE-AC36-99G010337