  Given the importance of clusters to the fields of cosmology and galaxy
evolution, it is critical to understand how the cluster detection process
affects (biases) ones scientific conclusions derived from a given cluster
sample. I review the astrophysics, algorithms, and observational constraints
that must be considered when attempting to assess cluster selection biases and
their impact on the scientific constraints derived from multi-wavelength
cluster surveys. In particular, one can more accurately quantify and understand
the selection biases and assess cluster evolution when using joint
optical/NIR/x-ray surveys than can be achieved when employing any single
cluster survey.
