  This chapter provides an overview of past and present techniques for optical
detection of galaxy clusters. It follows the progression of cluster detection
techniques through time, allowing readers to understand the development of the
field while explaining the variety of data and methodologies applied. Within
each section we describe the datasets and algorithms used, pointing out their
strengths and important limitations, especially with respect to the
characterizability of the resulting catalogs. The next section provides a
historical overview of pre-digital, photographic surveys that formed the basis
for most cluster studies until the start of the twenty-first century. Section
three describes the hybrid photo-digital surveys that created the largest
current cluster catalogs. The fourth section is devoted to fully digital
surveys, most specifically the Sloan Digital Sky Survey and the variety of
methods used for cluster detection. We also describe smaller surveys, mostly
for higher redshift systems. The fifth section gives an overview of the
different algorithms used by these surveys, with an eye towards future
improvements. The concluding section discusses various tests that remain to be
done to fully understand any of the catalogs produced by these surveys, so that
they can be compared to simulations.
