When you end a sentence with an abbreviation, you don’t need an extra period.

Apple Computer, Inc. became Apple, Inc.. (wrong)
Apple Computer, Inc. became Apple, Inc. (right)

The period that ends the abbreviation also ends the sentence. Think of it as an environmentally friendly rule—one dot of ink serves two purposes.

Even though such sentences are correct, they can confuse readers who may not realize you’ve ended the sentence. It’s best to write out the abbreviated word if it falls at the end of a sentence or to rewrite the sentence so the abbreviation doesn’t come at the end.

The story is different when the sentence is a question or exclamation—then you need both punctuation marks: