This document defines and provides examples of infinitives and infinitive phrases. It states that an infinitive is the word "to" plus a verb functioning as a noun or adjective/adverb. An infinitive phrase includes other words completing the infinitive's meaning, such as "to fly a plane". The document provides examples of infinitive phrases and distinguishes them from prepositional phrases. It includes warm-up exercises to identify infinitives and infinitive phrases in sentences.