Permanent account number requirement: PAN must be quoted in returns, payment challans and prescribed transaction documents. The substituted section 139A mandates allotment of a Permanent Account Number (PAN) to specified taxpayers and permits Assessing Officers to allot PANs more broadly; the Board may notify transition to a new-series PAN and require reapplication for persons in specified places. It compels quoting PAN in income-tax returns, payment challans and prescribed transaction documents, requires notification of changes to particulars, forbids possession of multiple PANs, and empowers the Board to make rules on application form, categories of documents and transactions. Definitions specify the Assessing Officer, PAN, and the new-series PAN form.