Cameron Chapman of Web Design Depot has written a heavily-illustrated article about the history of the ampersand. This old symbol has again become popular in the last several years with the emergence of abbreviated written communications, such as tweets and text messages.
The word "ampersand" was first added to dictionaries in 1837. The word was created as a slurred form of "and, per se and", which was what the alphabet ended with when recited in English-speaking schools. (Historically, "and per se" preceded any letter which was also a word in the alphabet, such as "I" or "A". And the ampersand symbol was originally the last character in the alphabet.)