This document discusses opinion mining and sentiment analysis. It begins with an introduction to the topic, explaining how people use blogs, forums and social media to share opinions. It then defines sentiment analysis as the automated extraction of subjective content and predicting sentiment from digital text. The document outlines the key components of sentiment analysis, including subjectivity, opinion definition and the components that are analyzed. It also discusses some common approaches to sentiment analysis and some of the main challenges, such as dealing with language, domain specificity, spam and named entity identification.