In this article, we show possibilities and limitations of the Fe-57-Mossbauer spectroscopy applied to iron-based pnictides and chalcogenides. The principle structure of these materials are FePn- or FeCh-layers with tetragonally coordinated Fe2+ ions. These layers are the electronically active structures for the competing magnetic and superconducting ground states. Mossbauer spectroscopy is frequently applied to investigate zero field local magnetic properties of both powder and single crystal materials. However, the absolute size of the hyperfine parameters often is small and the study can benefit from the application of an external field. With the help of an applied field it is possible to study magnetic interactions, ferromagnetic impurities, the sign of the electric field gradient (EFG) and magnetoelastic coupling. We show different aspects of applied magnetic field measurements and discuss results in iron-based pnictides and chalcogenides. (C) 2016 WILEY- VCH Verlag GmbH & Co. KGaA, Weinheim