In this tutorial we will present some recent approaches to modeling watermarking and data hiding as communication problems. We first overview the data hiding problem (large payload) and show how one can model it as a channel coding problem with side information. We further describe how several popular data-hiding techniques fit into this model and describe their performance. We also review the watermarking problem (low payload) and present recent efforts to design watermarking algorithms based on fundamentals of detection theory, estimation theory, game theory, and information theory in general.