Monocytes originate from progenitor cells in the bone marrow and traffic via the bloodstream to peripheral tissues. During both homeostasis and in responses to clear pathogens, circulating monocytes leave the bloodstream and migrate into tissues where they, following exposure to local growth factors, pro-inflammatory cytokines and microbial products, differentiate into macrophage or dendritic cell sub-populations. Type 1 diabetes (T1D) is a disease characterised by the elimination of the insulin producing β-cells in the pancreatic tissue through activation mainly of the adaptive immune system. In metabolic diseases, i.e. obesity, Type 2 diabetes (T2D) and diabetic complications, inflammation is mostly driven by macrophages and has been shown pivotal for disease progression even when blood glucose levels are well controlled. This review describes some current ideas and trends regarding the monocyte and macrophage involvement and their polarization in metabolic diseases that might open up novel therapeutic areas for the growing diabetic population.