Not Just Another Punctuation Mark
Use a semicolon to join two independent clauses that are not connected with a coordinating conjunction.
(Coordinating conjunctions are for, and, nor, but, or, yet, and so.)
Note: The independent clauses MUST be closely related!
The United States has more computers than any other country; its residents own more than 164 million of them.
Camels are impressive creatures; they are much larger than one might imagine.
The weather was very good for gardens this summer; our flowers bloomed more than any time I can remember.
It can join two independent clauses when the clauses are connected by a conjunctive adverb!
(Conjunctive adverbs are: as a result, for example, however, therefore, and instead.)
Japan is next on the list; however, the Japanese have only 50 million computers.
You might think that the billion people of China own a lot of computers; instead, the smaller country of Germany has twice as many computers as China.
Use a semicolon between groups of words in a series when one or more of the groups already contain commas.
Many of our community's residents separate their garbage into bins for newspapers, cardboard, and junk mail; glass, metal, and plastic, and nonrecyclable trash.