Primary protein energy malnutrition is malnutrition arising directly from a diet containing far too little protein and energy, as opposed to secondary malnutrition caused by disease, malabsorption, or increased needs. It takes two classic forms in children: marasmus, the wasting from overall energy deficiency, and kwashiorkor, the oedematous form linked to very low protein intake, though the two often overlap. Causes are fundamentally about food access: famine, poverty, war, and displacement, compounded by repeated infections that raise needs while suppressing appetite. Treatment follows staged protocols, stabilising with careful refeeding to avoid refeeding syndrome, then catch-up growth with energy- and protein-dense therapeutic foods like ready-to-use therapeutic food (RUTF). Prevention is agricultural, economic, and political: no clinical programme substitutes for households having enough nutritious food.