This study reports the development of a 19-item Flame Test Concept Inventory, an assessment tool to measure students' understanding of atomic emission. Fifty-two students enrolled in secondary and postsecondary chemistry courses were interviewed about atomic emission and explicitly asked to explain flame test demonstrations and energy level diagrams. Analysis of students' explanations offered insight into students' alternative conceptions and was used to design items and distractors for a 19-item Flame Test Concept Inventory about atomic emission. Results from a pilot study with first-year university chemistry and with upper-division chemistry students were analyzed to create a final version of the inventory that was administered to both secondary students (N = 459) and first-year university students (N = 100) who had completed formal instruction and course assessment about atomic emission. Analysis of student responses indicated the inventory generated valid and reliable data. Common alternative conceptions about atomic emission that remain postinstruction and their prevalence are discussed.