Herbaria are collections of preserved plants specimens, some of which date back to the 16th century. They are essential to botanical research, especially in systematics. They can also be important historical documents. The collections of Lewis and Clark, Carolus Linnaeus, and Charles Darwin, to name a few, are primary sources for the study of these individuals' work. Now many of these herbarium specimens are being scanned and the images are freely available on the Web. This article deals with how these online collections may be used in teaching about biology and its history. It will highlight the JSTOR Plant Science project which is making available electronically about two million plant specimens, many historically significant, as well as the entire runs of important plant journals. In addition, it will discuss other valuable online resources including how links to social media can bring the history of botany to 21st-century students.