Graptolithina is a class in the animal phylum Hemichordata, the members of which are known as graptolites. Graptolites are fossil colonial animals known chiefly from the Upper Cambrian through the Lower Carboniferous Periods. A possible early graptolite, Chaunograptus, is known from the Middle Cambrian.

Graptolites are common fossils and have a worldwide distribution. The preservation, quantity and gradual change of graptolites over a relatively short geologic time scale allows the fossils to be used to date strata of rocks throughout the world. They are important index fossils for dating Palaeozoic rocks as they evolved rapidly with time and formed many different species. The end-Ordovician extinction event eliminated most graptolites.

Most fossil graptolites look like tiny saw blades. However, well-preserved graptolites can be seen to be tubular in cross-section, with the "teeth of the saw" formed by short open branches from the main tube. Careful study of the microscopic structure of the tubes of graptolites shows that they are very similar to the tubes of small worm-shaped animals called pterobranchs.