For companies, it is vital to closely monitor the public reception of key events, such as product launches or press releases. With real-time access and easy accessibility of user-generated content on Twitter, it is now possible to do sentiment classification of tweets. Sometimes also called opinion mining, it is an active field of research in which several companies are already selling such services. As this shows that there obviously exists a market, we are motivated to use our classification muscles built in the last chapter to build our own home-grown sentiment classifier.