HYPE is a process algebra developed to model hybrid systems --- systems that show both continuous and discrete behaviour. It is novel because it allows for the modelling of individual flows which means that subcomponents can be modelled in terms of these flows and do not need to be described monolithically. I will introduce the process algebra, and demonstrate how the ordinary differential equations (ODEs) describing the continuous behaviour can be obtained from the labelled transition system. I will also talk about notions of semantic equivalence and compare HYPE to other hybrid system process algebras. This is joint work with Jane Hillston (University of Edinburgh) and Luca Bortolussi (University of Trieste).