A semicolon (;) offsets information more than a comma but less than a period.
Use to link independent clauses when a coordinating conjunction is not present:
She looked through the telescope and saw Mars shining back at her.
She looked through the telescope; Mars was shining back at her.
Use to clarify a long series or when the information in a series is offset by commas:
The prosecutor’s office indicted Jim Smith, 24, of Augusta, Georgia; Carl Willis, 20, and Dave Brown, 27, from Knoxville, Tennessee; and Brian Brianson, 25, from Duluth, Mississippi, on charges of having bland names.
Use to link independent clauses when a conjunction is present if excessive punctuation is present in the independent clauses:
He prepared the lamb, rice, potatoes and beets for a meal to be shared between friends, neighbors and colleagues; but he knew there would still be room for dessert, his famous chocolate, pecan and raspberry torte.
The Associated Press Stylebook recommends breaking such clauses into individual sentences.
Part of a series on punctuation.