The following definitions and examples are from ChompChomp.com. Grammar Bytes! Grammar Instruction with Attitude © by Robin L. Simmons All Rights Reserved.

 The first appropriate use of the semicolon is to connect two related sentences. The pattern looks like this: Complete sentence + ; + complete sentence. Here is an example: My eighty-one-year-old grandmother still rides her Harley motorcycle; her toy poodle balances in a basket between the handlebars.

 You can also team up a semicolon with a transition to connect two complete sentences that are close in meaning. The pattern looks like this: Complete sentence + ; + transition +, + complete sentence.  Check out this example: My father does not approve of his mother cruising around town on a Harley motorcycle; however, Grandma has never cared what anyone thinks.

 Finally, use the semicolon to avoid confusion when you have complicated lists of items. The pattern looks like this: Item +, + More Information + ; + Item +, + More Information + ; + and + Item +, + More Information  Read the following example: On a Harley motorcycle, my grandmother and her poodle have traveled to Anchorage, Alaska; San Francisco, California; and Tijuana, Mexico.

Keep these three things in mind when you use a semicolon:  The two main clauses that the semicolon joins should be closely related in meaning.  Don't capitalize the word that follows the semicolon unless that word is a proper noun, one that is always capitalized.  Limit your use of semicolons; you should not scatter them wantonly throughout your writing. Semicolons are like glasses of champagne; save them for special occasions.

Thanks to OWL, the Online Writing Lab from Purdue University, for the following information.

after a complete statement in order to introduce one or more directly related ideas, such as a series of directions, a list, or a quotation or other comment illustrating or explaining the statement. For Example:  The strategies of corporatist industrial unionism have proven ineffective: compromises and concessions have left labor in a weakened position in the new "flexible" economy.

 The daily newspaper contains four sections: news, sports, entertainment, and classified ads.

 He said he would be at home by 5:30 p.m.

 He always liked to refer to Genesis 1:18 when starting a speech.

Space once between a colon and the next word, when the colon is used between words. Do not space between numerals and a colon when a colon is used to mark time or ratios.