MOLLYNX is a new crystallographic tool developed to access a more precise description of the spin-dependent electron density of magnetic crystals, taking advantage of the richness of experimental information from high-resolution X-ray diffraction (XRD), unpolarized neutron (UND) and polarized neutron diffraction (PND). This new program is based either on the well known Hansen–Coppens multipolar model ( MOLLYNX -mult) or on a new expansion over a set of atomic orbitals ( MOLLYNX -orb). The main difference between the two models is the basis of the expansion: in MOLLYNX -mult the expansion is over atom centered real spherical harmonics, in MOLLYNX -orb the expansion is over a set of atomic orbitals with which mono and bicentric contributions are calculated. This new approach of MOLLYNX -orb can also be applied to nonmagnetic crystals. This paper summarizes the theoretical ground of two models and describes the first applications to organic, organometallic and inorganic magnetic materials