 McMillen had only expected the game to sell a few hundred copies when he released it on Steam . For the first few months of its release , sales were roughly a few hundred per day , but shortly thereafter , McMillen found sales suddenly were boosted , a fact he attributed to numerous Let 's Play videos that had been published by players to showcase the game and drove sales . By November 2012 , the game sold over one million copies , with at least one quarter of those having purchased the " Wrath of the Lamb " extension . As of July 2014 , the game has sold over 3 million copies . By July 2015 , following the release of Rebirth , the combined games had over 5 million units sold . The Binding of Isaac is said to be a contributing factor towards the growth of the roguelike genre since around 2010 , with its success paving the way for later games that used the roguelike formula , such as FTL : Faster Than Light and Don 't Starve . 
