Volume 49 number 1 (2021)
(Abstract only) There are still unsolved problems in understanding the evolution of type II Cepheids of the W Virginis class. Period changes of W Vir variables have the potential to provide insight into that evolution. We illustrate this by showing the observed period changes of three W Vir variables in globular clusters. V2 in M10 shows a long-term decrease in period. V3 in M10 shows a small period increase. Sometimes, as with V1 in M12, irregular period changes make it hard to determine the long-term trend of the period change.