The rules that assign a device to a risk class, which then determines the conformity assessment route and the level of notified body involvement. Under the MDR devices fall into classes I, IIa, IIb and III according to the rules in Annex VIII. Under the IVDR devices fall into classes A, B, C and D under a different Annex VIII rule set.
Reference: MDR Article 51 and Annex VIII; IVDR Article 47 and Annex VIII