The development of a nuclear facility needs careful planning, adequate preparation and substantial investment. This includes the establishment of a legislative and regulatory framework with provisions to assess the adequacy of nuclear security and authorize activities at nuclear facilities at key stages in their lifetimes. This publication provides guidance to regulatory bodies responsible for the nuclear security of nuclear facilities on the authorization process for the operation of such facilities and for related activities. The guidance addresses nuclear security aspects that may require regulatory authorization during different stages in the lifetime of a nuclear facility, identifies the elements included in applications for authorization by the applicant or operator in each of these stages, and provides guidance to the regulatory body on the review and assessment of these applications and on related inspections as a basis for authorization decisions.