Mossbauer spectroscopy not only offers information about the structural and electronic properties of iron centres in biomolecules but also about their dynamic behaviour. In order to apply this nuclear method to biologically relevant iron centres knowledge of nuclear and molecular physics is required. This review introduces the basic physical concepts of 57Fe-Mossbauer spectroscopy. The various oxidation and spin states of iron are discussed in a simple orbital frame. Aspects of the ligand field theory of paramagnetic molecules are introduced, and a review covering the iron centres in proteins which have been presently characterized is given. The review covers Mossbauer studies starting from heme proteins, continuing with the above-mentioned proteins containing di-nuclear iron clusters, iron storage proteins and iron-sulfur proteins, and concludes with the complex iron clusters of nitrogenase. The physical properties of the different forms of iron centres as well as their biological relevance are elaborated upon. The effects of electronic spin dynamics on the Mossbauer spectra are reviewed. In addition, the dynamics of the iron ion itself and how it can be studied by Mossbauer spectroscopy is discussed. An introduction into the recently developed technique using synchroton radiation which is also called Mossbauer spectroscopy in the time domain shall give an impression about the future developments in this field of spectroscopy.