This article highlights the challenging task teachers face in selecting vocabulary to teach. First, we briefly discuss three features of the English lexicon that are crucial to keep in mind when selecting vocabulary for instruction and three approaches that have been suggested. Then, we present a theoretically based approach called Selecting Words for Instruction from Texts (SWIT) that we developed and implemented in a vocabulary instruction research project. SWIT enables teachers to identify optimal words for instruction within three different categories (Essential, Valuable, Accessible, and Imported) and determine whether to provide Powerful Vocabulary Instruction, provide Brief Word Explanations, or guide students to Infer Meanings using context and morphology. Following that, we present detailed examples illustrating how teachers can use SWIT to identify and teach key vocabulary from a narrative text and from an informational text. The article ends with an appendix describing the research project in which we developed SWIT.