We present an overview of SPICA, the Space Infrared Telescope for Cosmology and Astrophysics, a world-class space observatory optimized for mid- and far-IR astronomy (from 5 to  ~210 μm) with a cryogenically cooled  ~3.2 m telescope (<6 K). Its high spatial resolution and unprecedented sensitivity in both photometry and spectroscopy modes will enable us to address a number of key problems in astronomy. SPICA’s large, cold aperture will provide a two order of magnitude sensitivity advantage over current far–IR facilities (λ > 30μm wavelength). In the present design, SPICA will carry mid-IR camera, spectrometers and coronagraph (by JAXA institutes) and a far-IR imager FTS-spectrometer, SAFARI (~34–210 μm, provided by an European/Canadian consortium lead by SRON). Complementary instruments such as a far-IR/submm spectrometer (proposed by NASA) are also being discussed. SPICA will be the only space observatory of its era to bridge the far–IR wavelength gap between JWST and ALMA, and carry out unique science not achievable at visible or submm wavelengths. In this contribution we summarize some of the scientific advances that will be made possible by the large increase in sensitivity compared to previous infrared space missions.