Microtubules are cylindrical organelles of varying length, an overall diameter of 25 nm, and a central hollow core of approximately 5 nm thick. They constitute one of three major structural components of the cytoskeleton and are found in almost all eukaryotic cells, where they perform a variety of essential functions, including chromosome movement, vesicular traffic, beating of cilia and flagella, and maintenance of cell form and morphogenesis. Although microtubules were discovered by transmission electron microscopy in the late 1950s, biophysical evidence for their dynamic structure and function in mitosis was obtained almost a decade earlier through polarizing microscopy. Research on the morphology and molecular structure of microtubules spans 3 decades and is now entering an exciting new "biophysical" era, as described in this issue.