Safety critical systems are embedded systems that, in cases of errors or failures, could cause injury or loss of human life. Systems such as flight control, automotive drive-by-wire, nuclear reactor management, or operating room heart-lung-bypass machines naturally come to mind. But devices as common as the power windows in your car are also safety-critical, as soon as you imagine a small child reaching out of the car window at a fast food drive-thru to get another packet of ketchup and accidentally leaning on the control switch making the window shut on the child’s arm, or worse. This paper examines the principles of safety critical systems design.