This volume collects a number of theoretical and experimental lectures on various aspects of transport and mixing of active and passive particles in geophysical flows. Transports in fluids can be approached from two complementary perspectives: in the Eulerian view of mixing, the focus is on the concentration field - advection stetches and folds the concentration field and sharpens the gradients, while diffusion smoothes the field. In the Langrangian view, fluid parcels are followed around as they move with the flow, experiencing chaotic or shastic motion. Both pictures are considered in the present lectures, with passive particles carried freely by the flow and reactive particles, where chemically or biologically induced reactions change the character of the particles.