This document discusses various data compression techniques. It begins by explaining why data compression is useful for optimizing storage space and transmission times. It then covers the concepts of entropy and lossless versus lossy compression methods. Specific lossless methods discussed include run-length encoding, Huffman coding, and Lempel-Ziv encoding. Lossy methods covered are JPEG for images, MPEG for video, and MP3 for audio. Key steps of each technique are outlined at a high level.