Cellular microtubules are mosaic polymers assembled from multiple ??-tubulin isoforms bearing chemically diverse posttranslational modifications. This tubulin diversity constitutes a combinatorial code that regulates microtubule interactions with cellular effectors and alters their intrinsic dynamic and mechanical properties. Cells generate stereotyped and complex tubulin modification patterns that are important for their specialized functions. Here we give a brief overview of the tubulin genetic and chemical diversity and highlight recent advances in our understanding of how the tubulin code regulates essential biological processes ranging from intracellular cargo transport, to cell division and cardiomyocyte contraction. Finally, we speculate on the molecular mechanisms for the generation and maintenance of the complex stereotyped modification patterns that form cellular microtubule mosaics.