Vocabulary knowledge contributes to comprehension, fluency, and student achievement. The goal of vocabulary instruction should be to build students' independent word-learning strategies. This article provides research and theory in support of nine key ideas about words and vocabulary instruction. These ideas are important for middle and secondary teachers to know and understand in order to provide sound vocabulary teaching across the content areas. Topics discussed include: (1) The English language and the consistency of its rules; (2) How language competence grows from oral to written; (3) How words are learned; (4) Multiple meanings; (5) Multisyllabic words; (6) The importance of teachers' modeling word consciousness and their own excitement about learning new words. For each key idea, the author provides several practical suggestions for classroom instruction, including strategies for individuals, small groups, and the whole class. Several websites for developing vocabulary as well as professional resources for teachers are suggested. (Contains 1 table and 2 figures.)