Block assessment procedure for search and requisition cases requires a prescribed return and specified determination and assessment process. Where a search or requisition occurs, the Assessing Officer must serve a notice requiring a prescribed return declaring total income including undisclosed income for the block period within a specified period; that return is treated under the relevant assessment framework, late or revised returns are restricted, and no separate preliminary notice is required. The Assessing Officer will determine income per the prescribed mechanism, apply specified procedural provisions, pass an assessment or reassessment excluding certain procedural sections, align block periods when proceedings derive from another person's search, and deal with seized or requisitioned assets under the designated asset-handling provision, following prior approval from senior officials before issuing the notice.