During World War II, Shannon worked at Bell Telephone Laboratories (Bell Labs), where he made significant contributions to cryptography. His work on breaking codes and securing communication channels was essential to the war effort. This experience directly influenced his later work on information theory.

Shannon published his seminal paper, 'A Mathematical Theory of Communication,' in the Bell System Technical Journal. This paper introduced the concept of information entropy, defined the fundamental limits of data compression and reliable communication, and established the field of information theory. The paper had a profound impact on diverse fields, including computer science, linguistics, and neuroscience.

Shannon published 'Communication Theory of Secrecy Systems,' a declassified version of his wartime work on cryptography. This paper established a mathematical framework for analyzing the security of cryptographic systems and introduced the concept of perfect secrecy.

Throughout the 1950s, Shannon continued to develop and refine the concepts of information theory. He explored topics such as rate-distortion theory, source coding, and channel coding. His work laid the groundwork for modern communication systems and data storage technologies.