Dana Porter Library (DP)
The Dana Porter Library (or DP, pronounced 'dip'), is the primary library on campus. It forms part of the University of Waterloo Library system, housing collections primarily for arts, humanities, and social sciences, and providing study and research services to students, faculty, and staff. Most students likely only recognise it as a fantastic study spot, but believe it or not, there are many books in it too.
History
The library was constructed in phases. With construction beginning in 1963, it opened in 1965 with only three floors. By the next year, three more floors were added. note: There are conflicting sources on whether the library was open when it had only three floors. Also I can't find any pictures of it with three floors. I think there might be one on the walls of the library elevators.

In 1967, the library was renamed to the 'Dana Porter Library' to pay tribute to Dana Porter, the university's first chancellor.
In 1970, the library had grown to its full size with 10 floors.
Trivia
- There's a famous myth that the architects of the library did not account for the weight of all the books, and thus the library is sinking. This is probably not true.
- While not acknowledged anywhere else, Needles Hall floor plans mention an underground tunnel to DP. This means that theoretically there's a way to get from DP to nearly anywhere else on campus without going outside. (although it's unclear if this is a service tunnel or something more meant for humans)
- When constructed, the library was one of the tallest buildings anywhere nearby, so it was naturally a great place to put radio equipment. In a pre-internet world, this allowed the University of Guelph and later McMaster to have a two-way video link to Waterloo over line-of-sight microwave radio, enabling graduate students to attend the same lectures. It required identical video-equipped classrooms on either side and cost $1-million in 1991, so about double that today. (source source source source source).