Microtubules create diverse arrays with specific cellular functions such as the mitotic spindle, cilia and bundles inside neurons. How microtubules are regulated to enable specific functions is not well understood. Recent work has shown that posttranslational modifications of the tubulin building blocks mark subpopulations of microtubules and selectively affect downstream microtubule-based functions. In this way, the tubulin modifications generate a "code" that can be read by microtubule-associated proteins in a manner analogous to how the histone code directs diverse chromatin functions. Here we review recent progress in understanding how the tubulin code is generated, maintained, and read by microtubule effectors.