Page protection is a feature of wiki software that allows administrators to restrict contributions to particular pages. For example, pages are frequently protected so that they can only be edited by administrators. Page protection affects tens of thousands of pages in English Wikipedia and renders many of Wikipedia's most visible pages uneditable by the vast majority of visitors. That said, page protection has attracted very little attention and is rarely taken into account by researchers. This note describes page protection and illustrates why it plays an important role in shaping user behavior on wikis. We also present a new longitudinal dataset of page protection events for English Wikipedia, the software used to produce it, and results from tests that support both the validity of the dataset and the impact of page protection on patterns of editing.