The colon ( : ) and semicolon ( ; ) are frequently used incorrectly in place of each other. The two punctuation marks serve very different purposes, and should not be used interchangeably.
Colon
A colon is used to give emphasis, present dialogue, introduce lists or text, and clarify composition titles.
Emphasis—Capitalize the first word after the colon only if it is a proper noun or the start of a complete sentence. (She had one love: Western Michigan University.)
Dialogue—Write the speaker's name, followed by a colon and his or her statement. (Reporter: What is the Western Edge? Dunn: It is a strategic plan for promoting student success.)
Introduce lists, text or tabular material—Capitalize the first word after the colon only if it is a proper noun or the start of a complete sentence. (Our future is dependent on three things: sustainability, diversity, and enhancing our strength and health.)
Clarify the titles of books, lectures and other compositions—Use a colon in titles that express two parallel ideas. The words on either side of the colon should be able to stand on their own. (He wrote "Crisis Management by Apology: Corporate Response to Allegations of Wrongdoing.")
Semicolon
A semicolon has two general uses: to clarify a series and to indicate two closely related sentences.
Series—If one or more elements in a series contain a comma, use semicolons to separate them. Include a semicolon before the final conjunction. (Members of the Western Jazz Quartet are Tom Knific, bassist; Trent Kynaston, saxophonist; Steve Zegree, pianist; and Tim Froncek, drummer.)
Two closely related sentences—For the most part, you should use a semicolon only where you could also use a period, but want to demonstrate a relationship between two complete sentences. (Good grades are integral to student success; a strong support network is also important.)