Principle objective of this article is to Define and Discuss on Long Run Supply. Here explain Long Run Supply in economics perspective. In long run, firms can vary their input factors. The ability to vary how much input factors in this long‐run allows for the chance that new firms will enter the market industry and that some recent firms will exit the market industry. New firms will end up being tempted to enter the market if some of the existing firms in the market industry are earning positive economical profits. For these factors, the number of firms in a perfectly competitive market is unlikely to be unchanged in the long run.