Following the natural progression of chapters, this chapter should focus on expression-level (word or phrase) sentiment classification, as the last two chapters were about document-level and sentence-level classifications. However, we leave that topic to Chapter 7. In this and the next chapter, we focus on aspect-based sentiment analysis (or opinion mining) to deal with the full sentiment analysis problem as defined in Section 2.1 – that is, classifying sentiments and extracting sentiment or opinion targets (entities and aspects).