This document provides an overview of digital watermarking techniques. It discusses how watermarking has evolved from earlier steganography methods and classifications of watermarking such as image, audio, and video watermarking. It also summarizes various watermarking techniques including spatial domain methods that directly modify pixel values, frequency domain methods that operate in transform domains like DCT and DWT, and spread spectrum techniques. Specific spatial and frequency domain techniques are described for image, audio, and video watermarking. The document concludes that watermarking continues to be an evolving topic with opportunities remaining to further develop fragile and semi-fragile techniques.