The term `Grid Computing' is relatively new and means a lot of di erent things to a lot of dif- ferent people[19]. It has been used as a buzzword for any new technology to do with computing, especially computer networking, and therefore it has been over-hyped as the solution to just about every computing problem. One of the goals of this paper is to give a clear de nition of what Grid Computing is and why it is required. Grid Computing, or Network Computing, is intended to provide computational power that is accessible in the same way that electricity is available from the electricity grid - you simply plug into it and do not need to worry about where the power is coming from or how it got there. The idea of Grid Computing is the same - if more computing power is required, spare cycles on other computers are used. This means that super-computer type power is accessible without the huge costs of super-computing, and that CPU cycles that would otherwise be wasted are put to good use. In fact, one of the major researchers into Grid Computing, Ian Foster from the University of Chicago says \grids are above all a mechanism for sharing resources", [13]. This means primarily sharing CPU time but also other things such as data les. Although this description sounds simple there are a number of problems with creating Grid systems - how do you access computers with di erent operating systems, how do you nd those computers to access and how do you make sure that you can trust others to run code on your machine? In fact, how do you encourage people to let others run code on their machines in the rst place? These questions, and many others, need to be answered for Grid Computing to succeed and they are also discussed in this paper.