An introduction to the positron science and the Slow Positron Facility in High Energy Accelerator Research Organization (KEK) is given. The Facility provides an intense slow positron beam based on a dedicated linac. The Positron and positronium (a hydrogen-like bound state of a positron and an electron) are unique probes for materials. Various standard techniques of the positron annihilation spectroscopy and those related to slow positron beams are described with some applications. After giving a brief history of the facility, its present status is reported together with some recent results. A future plan (not authorized yet) of the facility expecting 109 e+/s slow positron pulse- DC-beam (s) using a superconducting linac is also described.
