Electrons are injected into the NSLS storage rings from a 750 MeV booster synchrotron fed by a 120 MeV linac. The electrons are first produced in a 100 KeV triode electron gun. The gun is pulsed at the booster revolution period, 94.6 nsec, seven times per booster cycle. Each pulse is 5 nsec long and supplies about 17 microbunches in the linac. After acceleration in the linac, the beam is injected into the booster on seven successive turns. Multi-turn injection in the booster is accomplished in the following way: The beam is deflected into the booster by a septum magnet. The first linac pulse goes around the booster and returns to the injection point just as the second pulse is coming out of the septum. The two pulses merge into a booster bunch and continue to circulate. This process is repeated until all seven linac pulses are injected. During the injection process, the field of a pulsed magnet prevents the circulating beam from striking the septum. The field of the main booster magnets is also increasing slightly during injection to place each linac pulse on a slightly different orbit from its predecessors. After injection, the magnetic field of the booster increases to maintain a constant orbit radius as the radiofrequency accelerating cavity boosts the electron energy to 750 MeV. At maximum energy, a kicker magnet is pulsed to send the beam past a septum and into the X-Ray or VUV storage ring. After extraction, the booster magnets ramp down to their injection settings. The booster cycle takes 1.2 seconds from one injection to the next. In the future, the injection cycle will be decreased to 0.5 seconds and the maximum energy will be raised to 800 MeV for improved storage ring injection.