Most organizations and corporations have mission statements in one form or another. (A good business plan will always include one.)
Mission statements are often aspirational but also restrictive, by which I mean they can save the organization from the dreaded “mission creep.” (For a funny “Portlandia” (the TV show) based example of averted mission creep, see below.*)
First, here is a list of 50 county (or public) law library mission statements, courtesy of the 3 Geeks and a Law Blog.