[en] Studies on MnAs, and in particular of its magnetostructural phase transition, have a long history. As a promising material for ferromagnet/semiconductor hybrid structures with new challenges for solid state physics and electronic engineering, MnAs thin films recently came again into the focus of interest. This review summarizes the presently available knowledge about epitaxial growth of MnAs films in a variety of epitaxial orientations on differently oriented GaAs substrates, their interface formation, and the interrelated structural and magnetic properties. In situ growth studies using reflection-high energy electron diffraction and high-resolution x-ray diffraction as well as imaging of the growth morphology by scanning tunnelling microscopy provided a detailed understanding of the growth kinetics. The mismatch accommodation mechanisms elucidated by high-resolution transmission electron microscopy investigations explain how films of high quality can be grown despite a large and anisotropic misfit. Most extensively considered are structural and magnetic properties that are related to the strain evolution in the films during cooling after growth. In clear contrast to bulk MnAs, the structural phase transition in MnAs films exhibits a coexistence of the ferromagnetic α-phase and the paramagnetic β-phase over a wide range of temperatures and a thickness dependent thermal hysteresis. This strain-mediated phase coexistence has been studied in detail by x-ray diffraction and by imaging the magnetic structure using magnetic force microscopy and magnetic circular dichroism photoemission electron microscopy, and also theoretically. It depends in a characteristic manner on the epitaxial orientation. Using high-resolution x-ray diffraction data, it is shown that a unified mechanism explains the shift of the ferromagnetic transition temperature to higher values in as-grown MnAs films of appropriate epitaxial orientation, in MnAs films under external biaxial strain, and in MnAs clusters within a GaAs matrix. The improvement of the structural and magnetic properties of the films by a post-growth thermal annealing process is demonstrated