Three prototypes ordered initially; first prototype (SSSR-1974) flew 7 March 1975, with 11° wing sweepback and furnished in 100-seat local service form, with carry-on baggage and coat stowage fore and aft of cabin; second prototype (SSSR-1975, later SSSR-42304) had 23° sweepback and more cabin windows, representative of 120-seat version with three more rows of seats and no carry-on baggage areas; third prototype (SSSR-1976, later SSSR-42303) introduced small refinements; flight testing proved 23° wing superior; first series of production aircraft, built to replace some Aeroflot Tu-134, generally similar to SSSR-42303 as exhibited 1977 Paris Air Show; changes for production included substitution of four-wheel main landing gear bogies for twin-wheel units on prototypes; scheduled service on Aeroflot's Moscow-Krasnodar route began late 1980. Substantial redesign during one-year grounding after in-flight failure, June 1982.

Yak-42D introduced from second quarter of 1989 and currently manufactured by Saratov Aviation Plant (SAZ). Yak-42A and other versions have been produced in small numbers or been proposed.