Sentiment analysis is a set of statistical text mining procedures aimed at identifying and measuring opinions, beliefs, or personal judgments which are not based on rational reasoning, but on subjective emotions. The development and success of sentiment analysis is due to its application in almost every business and social domain since many human activities are influenced by opinions which affect people’s behaviour. Its success coincides with the spread in the use of social media and the big data revolution because, compared to a traditional survey, sentiment analysis has become a fast and inexpensive device to study social phenomena, and it can be used to explain and anticipate the dynamics of different events. For this reason, sentiment analysis poses not only technical challenges requiring further research, but also the need to find a balance between strengthening the oversight of data access and advancing scientific discoveries.