Walnut fruit is rich in vitamins, carbohydrates, minerals, proteins and unsaturated fats which promote human health. Walnut kernels also contain a very high amount of serotonin which is a neurotransmitter involved in regulating moods, feelings of happiness, sleep, anxiety and blood pressure. Walnut also has anti-cancer, anti-ageing, anti-tumour, anti-bacterial, anti-inflammatory and anti-fatigue effects. Walnut green husk (WGH) has also exhibited positive effects on the alleviation of fat disorders. This chapter introduces walnuts as a source of vitamins, protein, fat and carbohydrate, and outlines their health-promoting properties.