Learners of English as a Second Language are frequently confused about when to use prepositions. While some explanations offered in textbooks are satisfactory, more often they are unsatisfactory or completely lacking. An analysis of explanations revealed the underlying relationships represented in prepositions of location or proximity. With English prepositions of proximity ("by, near, next to, beside"), the degree of distance expressed by each can be thought of as forming a continuum from "next to" to "near." It is useful for students to experience concrete distances between objects in the classroom or use visual aids, and to solidify the concepts by making statements using the prepositions. Another group of prepositions often found difficult includes "at, on, and in." Exploiting the three-dimensional aspects of prepositions may help explain their use in expressing spatial relationships, and subsequently their temporal relationships. Testing the understanding of these prepositions can be accomplished by having students ask each other questions about pictures, make contrastive pairs, or write a group story in which each student adds a sentence using a new preposition. It is important for teachers to understand that examples alone, without sufficient semantic explanation and opportunities to transfer the knowledge to new contexts, will be ineffective in teaching language learners. (MSE)