In this chapter, we develop the quantization of free field theories, beginning with the canonical quantization of a simple mechanical model—a linear chain of identical masses connected by springs. This system illustrates how classical normal modes form the basis for quantized excitations, leading to the concept of phonons as quanta of lattice vibrations. We then promote classical coordinates and momenta to operators and replace Poisson brackets with commutation relations, revealing the structure of quantum harmonic oscillators. The resulting Hamiltonian describes an ensemble of independent oscillators with discrete energy levels, including the zero-point energy contribution. This framework provides the foundation for quantizing continuous fields, setting the stage for the treatment of free scalar fields and, ultimately, interacting quantum field theories.