Exoplanetary atmospheric retrieval refers to the inference of atmospheric properties of an exoplanet given an observed spectrum. The atmospheric properties include the chemical compositions, temperature profiles, clouds/hazes, and energy circulation. These properties, in turn, can provide key insights into the atmospheric physicochemical processes of exoplanets as well as their formation mechanisms. Major advancements in atmospheric retrieval have been made in the last decade, thanks to a combination of high-precision spectroscopic observations and advanced atmospheric modeling and statistical inference methods. These developments have resulted in key constraints on the atmospheric chemical abundances, temperature profiles, and other properties for a wide range of exoplanets. New spectrographs on state-of-the-art facilities such as the James Webb Space Telescope (JWST) and large ground-based telescopes are making important advances in this area. The present chapter aims to provide a pedagogical overview of this exciting frontier of exoplanetary science. The principles of atmospheric retrievals of exoplanets are discussed, including parametric models and statistical inference methods, along with a summary of key results in the field. Some of the main challenges in retrievals are discussed along with new directions in the future landscape.