Natural language processing is concerned with programming computers to process and analyze large amounts of natural language data. Sentiment analysis is a technique to detect subjective information in text documents by determining the sentiment of a writer about some aspect of a document. It recognizes the subjectivity and objectivity of text and classifies the opinion orientation. Sentiment analysis works by extracting features from text, preprocessing the text by stemming words and removing stop words, and then classifying the text sentiment using classifiers like Naive Bayes. The benefits of sentiment analysis include determining marketing strategy, improving products and customer service, using user input for mining, and improved decision making.