This thesis investigates the flows inside an evaporating, particle-laden liquid drop using the principles of fluid mechanics. In daily life, the flows in a coffee drop leaves behind a “coffee ring” on the table after the water evaporates. This thesis has found a new fluid mechanical mechanism in the evaporating drop that not only can generate the “coffee ring”, but also can separate particles in the drop according to their properties. The finding of this thesis leads to a new understanding of the physics of evaporating drops which will lead to new technological applications.