Although social media platforms serve diverse purposes, from social and professional networking to photo sharing and blogging, people frequently use them to share the thoughts and opinions and most importantly, their interests (e.g., politics, economy, sports). Understanding the interests of social media users is key to many applications that need to characterize them to recommend some services and find other individuals with similar interests. In this paper, we propose two approaches to the automatic determination of the interests of social media users. The first, that we named Frisk, is an unsupervised multilingual approach that determines the interests of a user from the explicit meaning of the words that occur in the user’s posts. The second, that we termed Ascertain, is a supervised approach that resorts to the hidden dimensions of the words that several studies indicated to be capable of revealing some of the psychological processes and personality traits of a person. In our evaluation, that we performed on two datasets obtained from Twitter, we show that Frisk is capable of inferring the interests in a multilingual context with good accuracy and that the psychological dimensions used by Ascertain are also good predictors of a user’s interests.