The electricity infrastructure is one of societys most critical infrastructures. The complexity of the electricity infrastructure system is increasing quickly, due to the increasing intensity of market-based power exchanges between electricity systems, the associated market restructuring and an increasing share of decentralized generation. As a consequence, the organizational complexity of power systems has exploded. At the same time, there is a shift in public and societal goals towards low-carbon and sustainable power generation. This will eventually require a drastic transformation of the industry. Increasingly, ICT is being depended upon for managing this infrastructure, for technical control and operation and for facilitating markets. A recent example is demand-side management, based on detailed metering of consumption and decentralized electricity generation.The mutual dependence of the electricity and the ICT infrastructures raises challenging questions in the areas of dependability, security and resilience. Examples include vulnerability to (cyber) attacks, avoiding and repairing technical failures and protecting data confidentiality, while guaranteeing accessibility. Therefore, better models and methods for protection against exploits of system vulnerabilities, whether accidental or intentional such as in cyber attacks, are called for.To address the above mentioned problems an advanced research workshop: 'Electricity security in the cyber age: Managing the increasing dependence of the electricity infrastructure on ICT' was organized in the Netherlands in May 2009. The objective of the workshop was to contribute to the security of current and future electricity infrastructures by analyzing the risks that are caused by the increasing reliance upon ICT and investigating options for managing these risks. The book presents the contributions to the workshop by distinguished invited keynote speakers and participants from the internationalscientific and industrial community.