This thesis investigates the quantum harmonic oscillator (QHO) through the path integral formulation. It begins with a review of classical dynamics and the standard operator approach to establish a foundational framework. The core of the work involves the systematic construction and evaluation of the QHO propagator, demonstrating how the transition amplitude naturally separates into a classical contribution and quantum fluctuations. Finally, the discussion extends to systems with infinite degrees of freedom, illustrating how the oscillator structure serves as a bridge to quantum field theory and the emergence of second quantization.