Primary adrenal insufficiency (Addison’s disease) refers to glucocorticoid deficiency resulting from adrenal gland disease. Central adrenal insufficiency is because of disorders of the pituitary gland (secondary) or the hypothalamus (tertiary). Long-term hypothalamic-pituitary-adrenal (HPA) axis suppression is commonly seen after chronic glucocorticoid therapy (iatrogenic). Transient HPA axis suppression is increasingly being reported in hospitalised patients with acute illness (relative adrenal insufficiency). This article extensively reviews various aetiologies and management of adrenal insufficiency.