Joint and several liability of partners ensures partners remain responsible for firm tax liabilities, with continued liability until retirement notice is received. Liability is joint and several for tax, interest or penalty: each partner and the firm are concurrently responsible. A retiring partner remains liable for liabilities up to the date of retirement whether determined or not, provided written notice of retirement is given to the Commissioner; if no such intimation is given within the prescribed period, the retiring partner's liability continues until the Commissioner receives the notice.