Research shows that there is a correlation between students’ vocabulary skills and reading comprehension. If students can pronounce words correctly, but they do not understand the meaning of words, their comprehension breaks down. This chapter first discusses how students learn new words through life experiences, vicarious experience, and explicit instruction. The explicit instruction occurs as teachers engage students in a study of word categories and word features. Students learn and “own” domain-specific words as they use the words in context when they are studying mathematics, science, social studies, and literature. One section of this chapter focuses on the semantic complexities of the English language, as words have multiple meanings. This chapter highlights the Common Core State Standards that focus on vocabulary building. Informal and formal vocabulary assessments are described in the “Assessment” section. The “Intervention” section describes activities for building younger and older students’ vocabularies. The “Technology” section lists apps and websites teachers can use to enhance students’ vocabulary growth. The chapter begins and ends with two different classroom scenarios with guiding and reflective questions that can be used for classroom discussions.