For both businesses and consumers, recommender systems have changed the face of online shopping, streaming and social media in the past two decades.

They predict user preferences and make recommendations of products or content they might like. And they are everywhere.

That list of products on Amazon "inspired by your shopping trends"? It's from a recommender system.

The list of videos on YouTube which are similar to the ones you have recently watched? A recommender system.

The "top picks for you" list of movies on Netflix? Also a recommender system.

A significant portion of profits from e-commerce businesses are generated by recommender systems. For example, according to a McKinsey study [1] in 2013, 35% of Amazon's sales came from recommendations. Nine years on, we can assume that proportion is even greater today.

In the retail sector, Amazon is - predictably - very much the market leader when it comes to recommender systems, having successfully introduced this technology in the 1990s.

These systems are constantly evolving as new methods and algorithms are discovered, not to mention data becoming available in increasing volume and variety. 

Ocula Technologies [2]