Machine learning applications for growing the world’s knowledge at Quora: At Quora our mission is to “share and grow the world’s knowledge”. We want to do this by getting the right questions to the right people to answer them, but also by getting the existing answers to people who are interested in them. In order to accomplish this we need to build a complex ecosystem where we value issues such as content quality, engagement, demand, interests, or reputation. It is not possible to build a system like this unless most of the process are highly automated and scalable. We are fortunate though to have lots of very good quality data on which to build machine learning solutions that can help address all of the previous requirements. In this talk I will describe some interesting uses of machine learning at Quora that range from different recommendation approaches such as personalized ranking to classifiers built to detect duplicate questions or spam. I will describe some of the modeling and feature engineering approaches that go into building these systems. I will also share some of the challenges faced when building such a large-scale knowledge base of human-generated knowledge.