One of the most cited definitions of interdependency is the one by Rinaldi et al. who define interdependency as a
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:
Empirical analysis of Critical infrastructure incidents and events by Van Eeten et al. 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
- 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
- PROTEZIONE DELLE INFRASTRUTTURE CRITICHE INFORMATIZZATE La realtà Italiana (2004)
- Comprehensive Disaster Management Policy Framework for Trinidad and Tobago
- [http://www.cnpic.es/Biblioteca/Legislacion/Generico/Ley_8-2011_PIC.pdf 7630 Ley 8/2011, de 28 de abril, por la que se establecen medidas para la protección de las infraestructuras críticas.
- DHS Risk Lexicon 2010 Edition, September 2010
- Critical Infrastructure Protection and Resilience Toolkit (Glossary), US Department of Homeland Security