Malnutrition is a global problem occurring in some 30% of all patients with active cancer and impacting on overall survival. Malnutrition today in many settings and in most places surveyed is underdiagnosed and undertreated. One reason is lack of dedicated nutrition education in medical schools and lack of universal screening protocols. While malnutrition endangers strength, daily activities, quality of life, immune competence and response as well as tolerance to anticancer therapies, recommended nutritional interventions include provision of adequate energy and nutrients, especially proteins, fats may be preferred over carbohydrates in settings of metabolic derangements and stimulation of muscle training should accompany all nutritional interventions. Recent ESPEN guidelines on nutrition in cancer patients will soon be complemented by ESMO guidelines on cancer cachexia. While many recommendations are similar in both guidelines, ESPEN provides more details on specialized nutritional interventions, ESMO focusses on adapting treatments to cachexia stages and highlights the requirements for multi-professional care.