Mononuclear phagocytes are the most common cells in the kidney associated with immunity and inflammation. While the presence of these cells in the kidney has been known for decades, the study of mononuclear phagocytes in the context of kidney function and dysfunction is still at an early stage. The purpose of this review is to summarize the current knowledge regarding classification of these cell in the mouse kidney and to identify relevant questions that would further advance the field and potentially lead to new opportunities for treatment of acute kidney injury and other kidney diseases.