The International Harvester S-Series was a range of medium and heavy duty trucks introduced in 1978. Previously, International had used the S-Series name for the 1956-1957 International Harvester S-Series, which consisted of light, medium, and heavy duty trucks. This new iteration of the S-Series only offered medium and heavy duty variants, consolidating the previous Loadstar and Fleetstar lines. Two generations of the S-Series were built, the First Generation from 1978 to 1989, and the Second Generation from 1990 to 2001. The first generation featured variant names beginning with S (ex. S1600), while the second generation dropped the S, and only featured number designation (ex. 4700). Production of the International Harvester S-Series Medium & Heavy Duty trucks lasted until 2001, when it was replaced by the International Harvester DuraStar.