Traditionally, molecular dynamics and Monte Carlo simulations of condensed phase systems including biopolymers are carried out using molecular mechanics or force fields that describe intermolecular interactions. In fact, the formalism of these force fields for biomolecular simulatiosn was established in the 1960s. Although the computational accuracy has increased enormously through parameterization, little has changed in the functional terms used in the force fields. In this talk, I will describe an explicit polarization (X-Pol) method based on quantum mechanics for developing force fields in condensed phase simulations. The theory, algorithm and application of this approach will be illustrated and its feasibility is demonstrated.