Paper on our vision for multiscale programming at the BCS Visions 2010 conference. Working with Richard Mortier, Jon Crowcroft, and Steven Hand, we presented a clean-slate approach to heterogeneous cloud computing that sweeps away decades of system software cruft. The paper argues that the move to virtual clouds creates an opportunity to build a unified platform spanning from cloud servers through desktops to mobile smartphones - this became the foundation for the Mirage framework. We demonstrated how this multiscale approach could deliver significant benefits in security, reliability and efficiency across the entire computing spectrum.