Macrophages are present in almost all tissues. They are contributing to various processes in the healthy organism, such as development, wound healing, infection and tissue homeostasis. They can rapidly change their phenotype in response to variations in their environment. Macrophages are known for their classical function as antimicrobial phagocytes but support immune function as well by the presentation of antigens. Their research applications are vast, and in vitro assays are increasingly used in a wide range of research areas, including immunology, bacteriology and parasitology, as well as in biomedical and transplantation studies. Two advantages of macrophages in cell culture are that they are relatively easy to generate and to cultivate.