This article explores the negotiation of safety between two distinct activity systems that operate jointly on a daily basis: train driving and railway traffic controlling. We have employed cultural-historical activity theory and an ethnographic case study of a large European passenger and freight transport company to pinpoint three different types of movement underpinning the negotiation of safety. These different movements can be found in work organization, work situations, and workers’ actions. The negotiation of safety would appear to be based on the movements of articulation (articulation, disarticulation, re-articulation), alignment (alignment, misalignment, realignment), and separation (separation, re-separation, de-separation) between activity systems. Within the framework of activity theory, we have used evidence from highly reliable organizations and the management of high-risk organizations to offer a better understanding of the movements between activity systems in safety negotiation.