This paper reports on an instrument designed to assess the practices and beliefs of instructors of introductory statistics courses across the disciplines. Funded by a grant from the National Science Foundation, this project developed, piloted, and gathered validity evidence for the Statistics Teaching Inventory (STI). The instrument consists of 50 items in six parts and is administered online. The development of the instrument and the gathering and analysis of validity evidence are described. Plans and suggestions for use of the STI are offered. (Contains 5 tables and 5 figures.)