Quantum mechanics is a fundamental theory in physics that describes the behavior of matter and energy at very small scales, such as atoms and subatomic particles. It introduces concepts like wave-particle duality, where particles can exhibit properties of both waves and particles, and superposition, where a particle can exist in multiple states at once until measured. One of the key principles of quantum mechanics is the uncertainty principle, formulated by Werner Heisenberg, which states that certain pairs of properties, like position and momentum, cannot be simultaneously known with arbitrary precision. This challenges classical physics and has led to advancements in technology, including quantum computing and quantum cryptography.