Return of income filing rules prescribe due dates, special disclosure duties, defective return treatment, and updated return restrictions. Section 139 requires specified assessees, including companies, firms, and other persons crossing the taxable threshold or meeting prescribed conditions, to furnish returns of income or loss by the due date in the prescribed form and manner. It also provides special filing obligations for persons with foreign assets, charitable and exempt institutions, political parties, business trusts, and investment funds, while laying down the due dates, treatment of defective and revised returns, interest for delay, and the updated return mechanism subject to statutory restrictions.