This circular contains the following: a) A generic introduction to the TEM framework, including definitions; components of the framework; threat and error countermeasures; and threats, errors and undesired states in relation to outcomes; b) A discussion on TEM in ATC, including definitions; threats in ATC; errors; undesired states; TEM-based analysis of actual ATC situations; managing threats and errors; TEM training for ATC personnel; integrating TEM in safety management; and Normal Operations Monitoring; etc.