The ability to detect micro expressions is an important skill for understanding a person’s true emotional state, however, these quick expressions are often difficult to detect. This is the first study to examine the effects of boundary factors such as training format, exposure, motivation, and reinforcement on the detection of micro expressions of emotion. A 3 (training type) by 3 (reinforcement) fixed factor design with three control groups was conducted, in which 306 participants were trained and evaluated immediately after exposure and at 3 and 6 weeks post-training. Training improved the recognition of micro expressions and the greatest success was found when a knowledgeable instructor facilitated the training and employed diverse training techniques such as description, practice and feedback (d’s > .30). Recommendations are offered for future training of micro expressions, which can be used in security, health, business, and intercultural contexts.