  Monitoring several correlated quality characteristics of a process is common
in modern manufacturing and service industries. Although a lot of attention has
been paid to monitoring the multivariate process mean, not many control charts
are available for monitoring the covariance matrix. This paper presents a
comprehensive overview of the literature on control charts for monitoring the
covariance matrix in a multivariate statistical process monitoring (MSPM)
framework. It classifies the research that has previously appeared in the
literature. We highlight the challenging areas for research and provide some
directions for future research.
