Activity Classifier classifies the activity of a person based on wrist worn accelerometer readings. These activities include walking, sitting, lying and climbing stairs. The classifier is implemented in Python using scikit-learn. Scikit-learn is a free software machine learning library for the Python programming language. This report includes the methodology adopted for training data set using different algorithms, a comparison of the performance of these algorithms and predictions made on unseen data by using of the algorithms whose performance was better than the other algorithms. The file Report.pdf contains further details about this project.