The Town of Arlington was originally settled in 1635 as a village called Menotomy. Over the years, the name has changed a few times. At one point, it was part of what was called West Cambridge but has been called Arlington since 1867.
In Massachusetts, there are two forms of municipal government. Boston, for example, is a city. There are 53 municipalities in Massachusetts organized a cities. Arlington, however, is a town, and there are 298 towns in Massachusetts. Massachusetts allows a specific form of town government called Town Meeting. It is a fascinating system and Wikipedia has a pretty good discussion of it here: http://en.wikipedia.org/wiki/Town_meeting#Massachusetts
For more about Massachusetts municipalities, the Massachusetts Municipal Association's website has a wealth of information: http://www.mma.org/
The Town of Arlington maintains an official website, which is a treasure trove of useful and interesting information for residents and visitors: http://www.arlingtonma.gov