A Mathematical Theory of Communication
Shannon established the mathematical foundations of information theory, modeling communication as the reproduction of a message selected from a set of possibilities across a (possibly noisy) channel. He introduced entropy as a quantitative measure of information and uncertainty, defined channel capacity, and proved coding theorems showing that reliable transmission is achievable up to (but not beyond) the channel capacity. The work unified the treatment of discrete and continuous sources and laid the groundwork for modern digital communication and data compression.