The emergence of taller buildings using engineered timber as a structural material raises important questions about the language that is used to describe tall buildings. In the absence of formal definitions it is difficult to make meaningful comparisons between buildings using different materials, structural systems and building forms. Claims to the title of 'tallest timber building' are frequently made and may be subject to dispute. This paper discusses the role of the CTBUH Criteria for Defining and Measuring Tall Buildings in the classification of tall buildings and the challenges to the existing criteria raised by the emergence of engineered timber as a contemporary structural material. The paper highlights the authors' proposal for updating the existing terminology to accommodate the use of timber in the design of tall buildings and details the progress that has been made in moving towards a revision of the CTBUH Criteria to include timber. This progress is significant as it represents a critical step forward in bringing timber engineering into the mainstream discourse of tall building construction and places timber on a level playing field with steel and concrete.