What is a Grid? More rapidly than any previous technology revolution, the Internet has come to play a central role in our daily lives at work and at play. From desktop PCs to mobile phones, getting rapid access to information on the web whenever and wherever we want it has become second nature. The Internet has become a utility much like the electricity grid we already take for granted. In the knowledge-based economy that Europe must become if it is to prosper in the 21st century we need a new Grid: a global infrastructure that supplies access to secure, dynamic, networked services that provide information and knowledge for anyone, anywhere and anytime. Such a Grid must be available, affordable and dependable and must provide access to computing, data and sensor resources through sophisticated applications built around cooperating services. Grid-enabled service-oriented architectures add a new dimension to the Internet — facilitating its transformation from an information utility to a knowledge utility. Over the next decade such architectures will be a key enabler of the knowledge economy in Europe. The Grid works by invisibly connecting a network of diverse resources, such as computers, data repositories, software programs, scientific instruments and more. Connecting such resources together, in itself, is not revolutionary — after all, every time you look up a page on the web you are connecting your PC to a computer somewhere else in the world. A Grid, however, allows you, for example, to tap into that computer’s processing power, rather than simply look at some of its files. Now add the power of a thousand other computers spread across a region, a country, or the globe. You choose how much power you want to use — your computational Grid parcels the job and shares it out to computers connected to it. Suddenly your PC has become a gateway to an invisible computing service infrastructure provided through the network and you only pay for the service you need, when you need it. But you have much more than that — you can also access massive amounts of data, whether they are stored in dedicated data storage devices or flowing from scientific instruments and or smart sensors. They are all attached to your data Grid which — thanks to the computing service infrastructure available in the network — can both process and store these data easily, using a whole range of software designed to make the most of the Grid’s computing power and distributed data. And more still — Grid services enable new sorts of software to become possible. Instead of huge amounts of data coming, for instance, from a web search, you now get access to knowledge, generated by semantic analysis software running on your knowledge Grid. A new generation of knowledge services that reach beyond the capabilities of today’s search engines will help you understand and process these data, providing you with instant access to answers to queries from across the world. Irrespective of whether your team is designing cars, creating animated films, seeking new medicines or modelling the Earth’s atmosphere, the basic principle is always the same: your Grid supplies all the resources, such as computing, storage, software, data and knowledge you need in one integrated service package, and helps project teams work more effectively together. The convergence between Grids, web services, semantic technologies and emerging service-oriented architectures will enable the provision of computing, data, information, and knowledge capabilities as utility-like services, thus fostering the emergence of service-oriented knowledge utilities in the 21st century.