The first implementation of a single photon avalanche diode (SPAD) is reported in 130nm CMOS technology. The SPAD is fabricated as p+/nwell junction with octagonal shape. Premature edge breakdown is prevented through a guard ring of p-well around the p+ anode. The dynamics of the new device are investigated using both active and passive quenching methods. Single photon detection is achieved by sensing the avalanche using a fast comparator. The SPAD exhibits a maximum photon detection probability of 41% and a typical dark count rate of 100kHz at room temperature. Thanks to its timing resolution of 144ps (FWHM), the SPAD can be used in disparate disciplines, including medical imaging, 3D vision, biophotonics, low-light-illumination imaging, etc.