diffcoeff.sty allows the easy and consistent writing of ordinary, partial and other derivatives of arbitrary (algebraic or numeric) order. For mixed partial derivatives, the total order of differentiation is calculated by the package. Optional arguments allow specification of points of evaluation (ordinary derivatives), or variables held constant (partial derivatives), and the placement of the differentiand (numerator or appended). The package is built on xtemplate, allowing systematic fine-tuning of the display and generation and use of variant forms (like derivatives built from D, \Delta or \delta). A command for differentials ensures the dx used in e.g. integrals is consistent with the form used in derivatives. The package requires the LaTeX3 bundles l3kernel and l3packages.