They also can be used to estimate various experimental observables, including solvation free energies of small molecules , binding free energies of small molecules to proteins and molecular hosts, and the on and off rate constants for noncovalent association events. Molecular simulation technologies rely on potential functions, or force fields, mathematical functions which estimate the energy of the molecular system and the forces on its atoms as a function of the atomic coordinates. The force field used in a simulation is a critical determinant of the accuracy of the results. The centrality of the force field has motivated decades of pioneering and innovative research and development. In spite of these efforts, recent studies indicate that force field issues still significantly limit the accuracy of simulations. The Open Force Field Initiative seeks a systematic approach to the continuing challenge of improving force fields, reducing the human effort required and generating new force fields that make statistically sound use of appropriate reference data. One major goal of our effort is to automate the development of new force fields given a choice of functional form and reference data. Later, we aim also to automate decisions about what functional forms to use and what reference data to fit. These capabilities will dramatically reduce the human time required to create new force fields, while also producing more accurate force fields with clear dependencies on the underlying data. Such capabilities would also support advances in force field science, such as determining what functional form achieves the best accuracy for particular applications at a specified level of computational cost. For example, a force field that explicitly treats electronic polarizability and includes fixed electric multipoles, such as AMOEBA, should be able to reach higher accuracy than a force field with fixed, atom-centered point partial charges. But how much additional accuracy do multipoles and polarizability actually provide? We cannot currently answer these questions because the question of the functional form is conflated with other issues, such as the use of different input data, different atom types, different fitting methods, and differences in the chemical intuition brought to the problem. In contrast, an automated approach would allow systematic evaluation of the benefits of an advanced functional form within a given context.