This document defines prepositions and discusses their types. Prepositions are words used before nouns or pronouns to indicate their relationship with other words. There are simple one-word prepositions and compound multi-word prepositions. Prepositions can also be categorized as prepositions of place, time, or direction depending on whether they indicate where something is, when something occurs, or where something is going. Examples are provided for each type of preposition.