The adult human body contains approximately 25 trillion red blood cells (RBCs), i.e., approximately 83% of the total sheer cell counts, as recent estimates suggest. Unlike other vertebrates (e.g., fish, amphibians, and birds), human RBCs lose their nuclei during their maturation process, an adaptation that favors the accumulation of ~250–270 million copies of hemoglobin per mature erythrocyte at the expenses of de novo protein synthesis capacity. As such, RBCs rely on mechanisms of adaptation through rapid changes in energy and redox metabolism following exposure to stimuli, from physiological or pathological hypoxia to oxidant stress. This chapter will provide an overview of red blood cell metabolism, from the basic essential pathways for energy generation (glycolysis) to the main antioxidant pathways (pentose phosphate pathway, glutathione homeostasis). Recent advancements in the field of mass spectrometry-based proteomics and metabolomics will be leveraged to discuss additional metabolic pathways that were originally thought to be absent or non-active in the mature erythrocyte. Since RBC transfusion is a lifesaving intervention for millions of recipients every year worldwide, the chapter will also review how RBC metabolism changes in response to the metabolic challenges that erythrocytes face under refrigerated storage conditions in the blood bank.