Recommendation Algorithms: Background Popularized by Amazon in the 1990s, recommendation algorithms have become a staple of business analytics. From shopping add-ons to information sharing via contact the influence of recommendation algorithms is undeniable. Under the hood, recommendation algorithms use both implicit (i.e number of times the item is purchased) and explicit (i.e star ratings) user feedback to determine the strength of association for a recommendation. I want to first define two main types of recommendation algorithms; content-based vs collaborative filtering.