Quantum mechanics, often referred to as quantum physics or quantum theory, is a fundamental branch of physics that revolutionized our understanding of the microscopic world. It is a theoretical framework that describes the behavior of particles at the atomic and subatomic levels, where classical physics fails to provide accurate predictions. Quantum mechanics has had a profound impact on science and technology, from our understanding of the behavior of electrons in atoms to the development of quantum computing. This essay provides an overview of quantum mechanics, its key principles, historical development, and some of its practical applications.