Oncoprotein 18/stathmin (stathmin) is a phosphorylation-controlled key regulator of microtubule dynamics. In recent years, substantial efforts were undertaken to characterize the complex formed between tubulin and the intrinsically disordered stathmin molecule. Here, I summarize and illustrate the current structural and thermodynamic studies on the tubulin-stathmin interaction. Based on these and on functional information I formulate an updated molecular mechanism on how tubulin-binding by stathmin regulates microtubule dynamics. (c) 2006 Elsevier Inc. All rights reserved.