Microtubules are dynamic cytoskeletal filaments that control different aspects of cell architecture. Microtubules are intrinsically asymmetric polymers, with fast-growing plus ends, which in cells serve as major sites of microtubule assembly and disassembly, and slow-growing minus ends, which are often stabilized and attached to different cellular structures. In my lab, we use in vitro assays combined with single molecule imaging to dissect how the proteins that bind to microtubule plus- and minus ends control microtubule nucleation and dynamics. In parallel, we employ live cell imaging to study how microtubules contribute to cell polarity, migration, division and differentiation. The combination of in vitro reconstitution assays with experiments in cells allows us to decipher how the specific molecular properties of microtubule regulators contribute to cellular function.