Ricci flow, Lie theory and sphere theorems Christoph Boehm (Muenster) Abstract: Using Ricci flow many sphere theorems have been proved in the last couple of years. In all these proofs it has been shown, that a sufficiently positively curved initial metric becomes rounder and rounder when envolved by the Ricci flow. We will explain how Lie theory can be used to show such a qualitative behavior.