This week, Friday the 27th of January, I will give a talk at USyd Carslaw 451 at 4pm on "Diffusion and anomalous diffusion in spatially extended systems" We present a universal view on the diffusive behaviour of the dynamics of spatially extended systems in anisotropic and isotropic media. We establish the existence of a nonlinear Huygens principle for weakly chaotic systems in isotropic media whereby the dynamics behaves diffusively in even space dimension and exhibits superdiffusive behaviour in odd space dimensions. This is joint work with Ian Melbourne.