This article describes the development of an instrument to measure teachers' knowledge of vocabulary development and instruction, the Teacher Knowledge of Vocabulary Survey (TKVS). This type of knowledge has become increasingly important as all classroom teachers are expected to help students meet language and literacy standards that include vocabulary acquisition. While a few studies have measured teacher knowledge of reading, there are no known instruments for measuring teachers' knowledge of vocabulary development and instruction. However, vocabulary is a crucial determinant of reading comprehension and content area knowledge, particularly for English learners (Graves, August, & Mancilla-Martinez, 2013). Statements about vocabulary development and instruction were gathered from foundational texts, reviewed by subject matter experts, and researched in cognitive labs for possible inclusion as items in the TKVS. The survey's 52 statements comprise 6 categories, including one section on vocabulary development, four sections on instruction, and one section on instruction specifically for English learners. Ratings of item difficulty by subject matter experts were then used to distinguish three levels of teacher knowledge of vocabulary: emergent, intermediate, and expert. Fifty teachers completed the TKVS, and their performance was found to correlate with the experts' predicted difficulties of the items. Initial analyses provide evidence for the content and construct validity of the TKVS as a measure of teacher knowledge of vocabulary development and effective instruction. The discussion considers implications for the use of the instrument, including as a needs assessment or guide for professional development for both preservice and inservice teachers.