The requirement that measurements be traceable to national standards arose in response to needs for consistency between different parts of the measurement system. There is no single agreed-upon definition for traceability, but it has been taken to mean the existence of some chain of inter-comparisons or calibrations leading back to the National Bureau of Standards. Like all procedural or material requirements, its presence or absence may bear little relation to the performance characteristic one is really interested in. The scientific problem of expressing the desired performance requirements in terms of the amount and type of evidence needed to determine the degree of consistency of measurement processes is discussed and illustrated for the measurement of temperature. The importance of the study of measurement as a production process and the need for a program for the surveillance of the measurement process is discussed and plans for a new service for transfer of measurement capability in thermometry are presented.