One of the most cited definitions of interdependency is the one by Rinaldi et al. who define interdependency as a
- 1 Definitions
- 2 Discussion
- 3 See also
- 4 Notes
- 5 References
This definition is adopted on the Commission's staff working document on a new approach to the EPCIP :
The working document also highlights that threats to a single Critical Infrastructure can have "a very significant impact on a broad range of actors in different infrastructures and more widely". The document also highlight the cross-border effect of interdependencies, spanning a number of European countries. The example identified in the document is the European high-voltage electricity grid, composed of the interconnected national high-voltage electricity grids.
European Project Definitions
The CIPRNet project  uses the following definition:
An older definition was:
Dependency and Interdependency can be defined as relationships which consider the cascading effect within sector/sub-sectors and/or across sectors/sub-sectors
The degree of interdependence does not need to be equal in both directions.
Empirical analysis of Critical infrastructure incidents and events by Van Eeten et al. , and again by Luiijf and Klaver (2021)  shows that interdependencies (= the mutual Dependency) hardly occur; and when they occur the effect is at a lower (weaker) dependency level.
- Steven M. Rinaldi, James P. Peerenboom, Terrence K. Kelly, Identifying, Understanding and Analysing Critical Infrastructure Interdependencies, IEEE Control Systems Magazine, December 2001, p.14.
- Staff Working Document on a new approach to the European Programme for Critical Infrastructure Protection - Making European Critical Infrastructures more secure, SWD(2013) 318 final, Brussels, 28.8.2013
- Glossary of the Government of Queensland
- NSW Critical Infrastructure Resilience Strategy Partner, Prepare, Provide (2018)
- GUIA DE REFERÊNCIA PARA A SEGURANÇA DAS INFRAESTRUTURAS CRÍTICAS DA INFORMAÇÃO Versão 01 (Nov. 2010).
- Protection of Critical Infrastructures – Baseline Protection Concept: Recommendation for Companies, BMI.
- UP KRITIS, BSI, 2014
- Strategic Emergency Management 2019
- PROTEZIONE DELLE INFRASTRUTTURE CRITICHE INFORMATIZZATE La realtà Italiana (2004)
- Comprehensive Disaster Management Policy Framework for Trinidad and Tobago
- 7630 Ley 8/2011, de 28 de abril, por la que se establecen medidas para la protección de las infraestructuras críticas.
- NIPP Directive (DHS Lexicon, 2010)
- DHS Risk Lexicon 2010 Edition, September 2010
- Critical Infrastructure Protection and Resilience Toolkit (Glossary), US Department of Homeland Security
- THE STATE AND THE THREAT OF CASCADING FAILURE ACROSS CRITICAL INFRASTRUCTURES: THE IMPLICATIONS OF EMPIRICAL EVIDENCE FROM MEDIA INCIDENT REPORTS, MICHEL VAN EETEN,ALBERT NIEUWENHUIJS,ERIC LUIIJF,MARIEKE KLAVER,EDITE CRUZ (2011)
- Analysis and lessons identified on critical infrastructures and dependencies from an empirical data set, Luiijf and Klaver, 2021