Run-on sentences and sentence fragments are common errors that occur when clauses are improperly joined or incomplete. A run-on sentence incorrectly connects two independent clauses without proper punctuation or conjunction. Sentence fragments lack a subject and verb and cannot stand alone. The document provides examples of run-on sentences and fragments, explains how they occur, and offers guidance on how to identify and correct them. Quizzes are included to help the reader practice identifying and fixing run-on sentences.