  The concept of states of financial markets based on correlations has gained
increasing attention during the last 10 years. We propose to retrace some
important steps up to 2018, and then give a more detailed view of recent
developments that attempt to make the use of this more practical. Finally, we
try to give a glimpse to the future proposing the analysis of trajectories in
correlation matrix space directly or in terms of symbolic dynamics as well as
attempts to analyze the clusters that make up the states in a random matrix
context.
