Users of financial statements usually seek to identify trends in the entity's financial position, performance, and cash flows by studying and analyzing the information contained in those statements. It is imperative that the same accounting policies be applied from year to year in the preparation of financial statements, and that any necessary departures from this rule be clearly disclosed. This fundamental theorem explains why IFRS requires restatement of prior periods' financial statements for corrections of accounting errors and retrospective application of new accounting principles. IAS 8 is applied in the selection of accounting policies and in the accounting for changes in accounting policies, changes in estimates and corrections of prior year errors. This chapter addresses the criteria for selecting and changing accounting policies, together with the accounting treatment and disclosure of changes in accounting policies, changes in accounting estimates, and corrections of errors in accordance with IAS 8.