This paper compares the dynamics of the process by which geographical clusters emerge in the US and UK computer industries, by modelling the evolution of firm growth and entry. In both countries, new companies are attracted by industry strength in particular sub-sectors in a particular region. Moreover, incumbent firms located in a cluster that is strong in their own sub-sector of the industry tend to grow faster than average. While there are some second order differences between the models estimated for the US and the UK, it appears that the dynamics of clustering are similar. In particular, there is no evidence that clustering effects are weaker in the UK than in the US.