  In this paper, we briefly review the development of ranking-and-selection
(R&S) in the past 70 years, especially the theoretical achievements and
practical applications in the last 20 years. Different from the frequentist and
Bayesian classifications adopted by Kim and Nelson (2006b) and Chick (2006) in
their review articles, we categorize existing R&S procedures into
fixed-precision and fixed-budget procedures, as in Hunter and Nelson (2017). We
show that these two categories of procedures essentially differ in the
underlying methodological formulations, i.e., they are built on hypothesis
testing and dynamic-programming, respectively. In light of this variation, we
review in detail some well-known procedures in the literature and show how they
fit into these two formulations. In addition, we discuss the use of R&S
procedures in solving various practical problems and propose what we think are
the important research questions in the field.
