According to Wikipedia, a mission statement is intended to "guide the actions of the organization, spell out its overall goal, provide a path, [and] the framework or context within which the company's strategies are formulated."
Most companies have one, but they're all a waste of time and mental energy. Here's why:
1. They're group-written.
When a group tries to write something in a corporate setting, the result is the lowest common denominator for every issue in the room. The process removes any statement that has an edge, resulting in digested wads of verbal pap.
2. They're full of platitudes.
Most mission statements read something like this: "We are committed to delighting our customers by creating the best products and offering them for the best price along the best customer service." Every company makes these same promises, so why bother?
3. They're full of abstractions.
Mission statements usually contain multiple words that are so vague as to be utterly meaningless. Take "best customer service," for instance. What exactly what does "best" mean in this context? There's no way to measure "bestness," so nobody knows.
4. They don't inspire or motivate.
Human beings are motivated by stories that contain meaningful emotional content, typically about people who overcome big obstacles to achieve difficult goals. Mission statements are just opinions and promises. Big shrug.
5. They're SO 1980s.
The entire "mission-statement" concept has a dress-for-success-while-searching-for-excellence-in-reengineering-your-corporation-which-is-named-something-that-sounds-like-"velocity" vibe to it.
6. They're mostly honored in the breach.
Talking about something is the opposite of doing something about it. Ever notice how it's the companies that have awful customer service that go on and on and on about how their customer service is so wonderful?
7. Nobody reads them.
Honestly, does anyone ever actually read these things? With a straight face, I mean? In short, if your company has a "mission statement," my best advice is to throw the posters in the trash, wipe it from your website, and pretend you never had one.