Mixing is a common phenomenon in everyday life. A blob of white cream placed in a cup of black coffee and gently stirred with a spoon forms, if one looks carefully, intricately shaped striated structures, until the mixture of coffee and cream homogenizes into a fluid that is uniformly brown in colour. This common phenomenon serves to illustrate some of the key features of mixing; namely, the interplay between advection and diffusion. If the coffee is at rest when the cream is added (and assuming that the insertion of the cream into the coffee only causes negligible disturbance of the surrounding coffee) then, in the absence of stirring, the cream mixes with the coffee by the mechanism of molecular diffusion. Experience tells us that in this particular situation the mixing takes much longer than we would typically be willing to wait. Therefore we stir the admixture of coffee and cream with a spoon, and observe it to homogenize very quickly. This stirring illustrates the role that advection plays in homogenizing the cream and coffee. In fact, in this particular example (as well as many others) the role of molecular diffusion in achieving the desired final mixed state may very well be negligible.