Classical mechanics is based on deterministic laws governing macroscopic objects, while quantum mechanics introduces probabilistic behavior at the atomic and subatomic levels. Key differences include the concept of superposition in quantum mechanics, where particles can exist in multiple states simultaneously, contrasting with classical mechanics' definite states. Additionally, quantum mechanics incorporates wave-particle duality, illustrating that particles exhibit both wave-like and particle-like properties. The role of observation is also crucial in quantum mechanics, affecting the state of a system, unlike in classical mechanics. Understanding these distinctions is essential for grasping the foundational principles of modern physics.