Defining what is “unique” about a book can take many forms as seen in the range of posts on this blog to date. Since I started at Penn though I’ve been especially eager to discover and make known those books in our collections which are unique in the purely quantitative sense – i.e. books where Penn’s copy is the only known example of a work. To this end, I’ve worked with data from the English Short Title Catalog to determine which of the Penn Libraries pre-1800 printed books are unique to Penn. Last week I posted a piece about what I found and I thought it might be of interest to those who read Unique at Penn. One of the reasons for identifying these unique works is to encourage their use by scholars and others at Penn and I would love to see additional work and interest on these titles by anyone out there!