The Astronomical Almanac is a widely used reference publication that provides astronomical data and information for astronomers, scientists, engineers, and students. First published in 1961, the almanac has become an essential tool for anyone interested in astronomy and space science. The Explanatory Supplement to the Astronomical Almanac (ESA) is a companion volume to the almanac, offering detailed explanations and descriptions of the data, formulas, and techniques used in the almanac. This article provides an in-depth review of the Explanatory Supplement to the Astronomical Almanac, focusing on its contents, significance, and utility.