The Exeter Book is a book containing Old English poetry that was given to Exeter Cathedral in 1072 by Leofric, the Bishop of Exeter. (1)
The book still remains there today in a locked room, though not in perfect condition(it had served as a cutting board and a beer mat and has had 14 pages burnt). It was written by a single man. (2) It contains 95 riddles and a few other writings such as The Fortunes of Men, The Panther, or The Whale. (3)
Most riddles are somewhere between 7 and 15 lines long, with a couple as short as 4 lines (Riddle 18) and some as long as 71-line Riddle 3 (3). The attached poems and other writings are generally much longer, sometimes more than 1000 lines.

The first page of "The Wanderer," from the Exeter Book. This is a poem, which looks like prose except for the lines in poetry which were defined by slightly larger gaps between words. These gaps, known as casurae, are visible if you look very closely (5)
Its parchment leaves measure about 12.5 inches by 8.6 inches, slightly larger than a standard sheet of American paper, and the book originally probably contained a total of 131 leaves. It probably was written by a single scribe. At some time after Leofric's donation, but before its first study by a Renaissance antiquary named John Joscelyn, someone bound an additional eight leaves to its front, but also, the original first eight leaves were torn out, leaving the first original text (the hymn "Christ") lacking its beginning. (6)

This is a picture of a page in The Exeter Book, in Old English. (7)
Sources1.
http://www.engl.virginia.edu/OE/Tour/Manuscript.images/Widsith.html2.
http://penelope.uchicago.edu/~grout/encyclopaedia_romana/britannia/anglo-saxon/flowers/exeter.html3.
http://www.georgetown.edu/labyrinth/library/oe/exeter.html4.
http://www.public.iastate.edu/~gbetcher/373/ExeterBk.htm5.
http://faculty.goucher.edu/eng211/exeter_book_and_wanderer.htm6.
http://faculty.goucher.edu/eng211/exeter_book_and_wanderer.htm7.
http://www.medieval.unimelb.edu.au/bernard/pics/eb1.jpg