{Compatibility in the world of \LaTeX} {Frank Mittelbach} {In this talk I take a look at the major disruptions that have rocked the \LaTeX{} world in the past decades and how we handled them, covering some of the resulting consequences. In the latest part of this saga a rollback concept for the \LaTeX{} kernel was introduced (around 2015). Providing this feature allowed us to make corrections to the software (which more or less didn't happen for nearly two decades) while continuing to maintain backward compatibility to the highest degree. I will give some explanation on how we have now extended this concept to the world of packages and classes which was not covered initially. As the classes and the extension packages have different requirements compared to the kernel, the approach is different (and simplified). This should make it easy for package developers to apply it to their packages and authors to use when necessary. }