Article 143 empowers the Tax Authority to issue 'best judgment' assessments based on estimation in four scenarios: (1) a return fails to meet legal conditions or lacks audited accounts; (2) no return was submitted; (3) an investigation reveals taxable income was omitted; or (4) the taxpayer requests an assessment (within three years of filing). This provision ensures the Authority can determine a tax liability even when a taxpayer is non-compliant or provides incomplete data. It shifts the burden to the taxpayer to maintain proper records to avoid an unfavorable estimated tax bill.