This Safety Guide recommends how the requirements established in Safety Standards Series No. NS-R-1, Safety of Nuclear Power Plants: Design (2000), should be met for instrumentation and control (I & C) systems important to safety. It supersedes Safety Series No. 50-SG-D3, Protection Systems and Related Features in Nuclear Power Plants (1980) and No. 50-SG-D8, Safety Related instrumentation and Control Systems for Nuclear Power Plants (1984).