Patients with nephrotic syndrome (NS) present with edema, proteinuria, hypoalbuminemia, and hyperlipidemia. In children, the most common causes are idiopathic minimal change disease and focal segmental glomerulosclerosis (FSGS). In adults, FSGS and membranous nephropathy (MN) are the most common primary causes. There are numerous secondary causes, including diabetes, amyloidosis, systemic lupus erythematosus, hematologic malignancies, and infections. In addition to confirming the diagnosis of NS by measuring proteinuria and serum albumin and lipid levels, evaluation should assess for secondary causes. In children, most cases are due to minimal change disease, which is responsive to steroid treatment. A glucocorticoid should be prescribed for children younger than 12 years. If the patient improves with steroid treatment, no biopsy is needed. If the patient does not improve, genetic testing and kidney biopsy are warranted to determine the diagnosis. In adults, biopsy typically is indicated for diagnosis, except in patients with positive test results for serum anti-phospholipase A2 receptor antibodies. This is diagnostic of MN. For patients with NS, management of initial and infrequent recurrences involves reduction of proteinuria with glucocorticoids. Frequent recurrences and/or the inability to discontinue glucocorticoids requires alternative therapies. Steroid-resistant NS also requires use of alternative therapies. Long-term NS management includes dietary sodium restriction, edema management, and blood pressure control. Thromboembolism prophylaxis should be considered for patients with NS and high risk of thromboembolism, particularly those with MN.