Macrophages are the most specialized phagocytic cells, and acquire specific phenotypes and functions in response to a variety of external triggers. Culture of bone marrow-derived or peritoneal macrophages from mice represents an exceptionally powerful technique to investigate macrophage phenotypes and functions in response to specific stimuli, resembling as much as possible the conditions observed in various pathophysiological settings. This chapter outlines protocols used to isolate and culture murine bone marrow-derived and peritoneal macrophages. Furthermore, we describe how these macrophages can be “polarized” to obtain specific macrophage subsets with special relevance to atherosclerosis.