Presentation I gave at the Auckland Bioengineering Institute's Friday Forum on 26th of September 2014. Described a bit of background as to why modularity and reuse is important in modelling of biological systems and how CellML provides facilities to enable modellers to make use of modularity and reuse in their model descriptions. Also talked about how the Physiome Repository provides tools to help users manage their modular model descriptions and reuse them across projects.