In this paper we: present fundamental studies elucidating the role of entro
py in particle suspensions. We focus on systems composed of large colloidal
particles along with a second, usually smaller species such as a particle
or polymer. We describe direct measurements of these interactions in suspen
sion, and we systematically show how these forces can be used to control th
e self-assembly of colloidal particles. The paper provides a unified review
of the experiments from our laboratory, and in a few cases touches on very
recent results.