Magnesium and its alloys are promising materials for biodegradable implant applications. However, the degradation rate in the biological environment should be adjusted for the specific application, to match the healing behavior of the surrounding tissue. For the control of corrosion, research has targeted development of new alloys as well as coatings and surface modification of Mg. This presentation will discuss challenges in developing suitable coatings for Mg for biomedical applications. The requirements for such coatings are multifunctional, in that the coatings should be biocompatible, biodegradable and optionally in addition bioactive. Different approaches to fulfill these goals have been explored, such as coatings based on biodegradable synthetic or natural biopolymers. The presentation will describe methods to successfully coat highly reactive Mg alloy surface in aqueous solutions, based on developing suitable pre-treatments of the surface. Immersion testing and electrochemical experiments revealed information on the corrosion protection properties of the coatings as well as on the time-dependent degradation of the coatings. Influence of the electrolyte composition on the performance of the coatings was studied, including the effect of proteins on the corrosion behavior. The exact composition of the type of simulated body solution as well as addition of proteins can very strongly influence the corrosion behavior. The effects are highly complex in that for instance proteins show a time-dependent and strongly system-dependent influence on the corrosion rate.