I had no sense of how much research has been done on sentiment analysis, opinion mining, and machine learning. I suppose major progress had to wait until there were massive datasets of text content available to process. The explosion of data on social media has provided both the impetus and the fodder to develop increasingly sophisticated techniques that are beginning to actually work. In this annotation I present an overview of the techniques and tools of comparative opinion mining. It's great to know what people feel and think about one thing. It's probably twice as great to know what they think about two things. Like two different cars, guitars, or political candidates.