Between the empiricism of typical classical force fields and the accurate, yet expensive, ab initio derived force fields, increasing attention is being drawn to mapping physically motivated parameters from QM into simple MM functional forms. By deriving bespoke force field parameters for the molecule under study directly from QM, the number of transferable, empirical parameters to be fit is significantly reduced. By retaining common MM functional forms, the potentials may readily be implemented in widely used MM software and used in, for example, free energy calculations. Bespoke intramolecular bond, angle and, particularly, torsion parameters may be readily derived from a small number of QM calculations either by fitting to Hessian matrices or potential energy surface scans. Atom-centred partial charges can be routinely derived from either semi-empirical calculations, or QM electrostatic potential fitting, or atoms-in-molecule electron density partitioning. Less common, but perhaps most interestingly, is the possibility of using atoms-in-molecule electron density partitioning to derive other components of the non-bonded interaction from QM, in particular dispersion coefficients (C 6 , 27-30 C 8 , ...), atomic polarisabilities, and off-centre charges to model electronic anisotropy. For example, Visscher and Geerke have derived a polarisable force field model, with a higher order dispersion term derived from iterative Hirshfeld atoms-in-molecule analysis, and applied it to small-molecule amino acid analogues. Of the 138 nonbonded parameters in their model, 132 are determined from QM, leaving just six to be fit to experiment. Kantonen et al employ a mapping of information from minimal basis iterative stockholder (MBIS) atomic electron densities (in particular the decay constants of the electron densities), to derive atom-specific Lennard-Jones parameters.