The perpetration of a cyber operation implies the involvement of one or more human perpetrators and computer systems. On the one hand, computer systems may be used for the creation, launch or transit of cyber operations. On the other, there is always a human involved in the perpetration of cyber operations, even when they imply a large level of automation. This observation is also true for state-conducted or state-sponsored cyber operations. As an abstract entity, a State must rely on human perpetrators to act on its behalf. This chapter, dedicated to the question of attribution, thus focuses on attribution to computer systems and to the individuals involved in the creation, launch or transit of cyber operations. These attribution processes are mainly technical and based on forensic analysis.