This document summarizes research on using data mining techniques to perform sentiment analysis on tweets. The researchers collected tweets from Twitter and preprocessed the text to make it usable for building sentiment classifiers. They used three classifiers - K-Nearest Neighbor, Naive Bayes, and Decision Tree - and compared the results to determine which provided the best accuracy. Rapid Miner tool was used to preprocess the text, build the classifiers, and analyze the results. The goal was to determine people's sentiments expressed in their tweets and correctly classify them.