Who has primary responsibility for the implementation of security controls? Response:

The Information System Owner (ISO) is accountable for the system throughout its lifecycle, including ensuring that security controls are properly implemented, operated, and maintained to meet security requirements. While other roles assist, the ISO has the ultimate primary responsibility for these actions.

An Information System Security Engineer designs and implements security solutions but does not hold primary responsibility for the overall implementation of controls across the system's lifecycle.

A System Administrator is responsible for the technical operation and maintenance of systems, including some security controls, but not the overarching primary responsibility for their implementation.

The Authorizing Official (AO) makes the risk-based decision to authorize a system's operation but does not have primary responsibility for the hands-on implementation of security controls.