The article examines critical infrastructure security from the perspective of institutional resilience, which encompasses not only technical solutions but also the less visible mechanisms shaping the functioning of organisations responsible for crisis management. The point of departure is the assumption that the ability to maintain essential functions under disruptive conditions results not only from formal procedures, but also from practices of action, relationships, and tacit knowledge which remain only partially regulated and standardised. The aim of the article is to demonstrate that the hidden dimension of resilience remains central to critical infrastructure security, despite being frequently marginalised in security policies. The working hypothesis assumes that infrastructure security depends on the capacity of institutions to operate under uncertainty, and particularly on silent institutional resilience, which manifests itself beyond formal procedures. The research method applied is a qualitative analysis of the literature combined with case studies of selected crisis situations. The findings indicate that informal relations, adaptive capacity, practical staff knowledge and local cooperation networks constitute a key component of resilience, and their development requires long-term organisational processes.