Nuclear beta decay provides a sensitive and rich tool for studying the structure of atomic nuclei as well as assessing the limits of our understanding of the weak interaction. In this chapter the history of the topic is presented. The main quantities associated with beta-decay spectroscopy are defined. Nuclear structure studies are illustrated by some selected examples of the beta decay of exotic nuclei, also aimed at presenting the most up-to-date techniques. The examples include the decay of 52Ni, 100Sn, and 132Sn and a discussion about the islands of inversion. The studies of the structure of the weak interaction and the tests of fundamental symmetries are illustrated through the most precise measurement of spectroscopic quantities and correlation terms, which have the largest impact on searches for new physics beyond the standard electroweak model. These measurements are motivated by the extraction of the strength of the weak interaction, the search for exotic couplings, and tests of parity and time-reversal symmetries.