A modified version of the first Soyuz spacecraft was designed for manned circumlunar flight.  None of the Zond ("probe") missions were ever actually manned, although early plans did call for Zond 7 to have a crew. Ultimately, 3 manned circumlunar missions were to have occurred.

Zond 4 (Zond 1-3 were versions of unmanned probes to Venus and had nothing to do with the circumlunar Zond's) was launched into a high (330,000 km apogee) orbit 180 degrees away from the moon. The guidance system failed and self-destruct was initiated.

Zond 5 did fly a successful circumlunar mission. Upon reentry, the gyroscope was disabled and the capsule came in at 20G's. It was recovered.

Zond 6 in November of 1968 also completed a circumlunar mission. Gasket failure caused a depressurization of the (unoccupied) crew compartment.

Zond 7 was originally scheduled for early December of 1968. A decision on whether or not to man this mission was to have been made around December 1. Technical difficulties delayed the flight into January. By that time, the United States had already flown Apollo 8 around the moon. The Soviets decided not to fly any of the manned circumlunar flights. Zond 7 finally did fly, unmanned, in August of 1969. It was the only Zond flight which could have gotten a crew back to Earth unharmed.

Zond 8 was flown as a purely research circumlunar mission in October of 1970. As had happened before, the guidance system failed and reentry was at 20G's.

Three planned manned circumlunar missions were scrubbed after Apollo 8. These would have been:
March 1969, Leonov and Makarov
May 1969, Bykovsky and Rukavishnikov
July 1969, Popovich and Sevastyanov