  An analogy between combinatorial chemistry and Monte Carlo computer
simulation is pursued. Examples of how to design libraries for both materials
discovery and protein molecular evolution are given. For materials discovery,
the concept of library redesign, or the use previous experiments to guide the
design of new experiments, is introduced. For molecular evolution, examples of
how to use ``biased'' Monte Carlo to search the protein sequence space are
given. Chemical information, whether intuition, theoretical calculations, or
database statistics, can be naturally incorporated as an a priori bias in the
Monte Carlo approach to library design in combinatorial chemistry. In this
sense, combinatorial chemistry can be viewed as an extension of traditional
chemical synthesis.
