The Character Compatibility Problem is a classical problem in computat
ional biology concerned with constructing phylogenetic trees of minimu
m possible evolution from qualitative character sets. This problem aro
se in the 1970s, and until recently the only cases for which efficient
algorithms were found were for binary (i.e. two-state) characters and
for two characters at a time, while the complexity of the general pro
blem remained open. In this paper we will discuss the remarkable progr
ess on this problem since 1990.