Emotion is understudied in nonhuman animals despite broad interests in the topic. This is partly due to the difficulty in measuring subtle emotional reactions, such as physiological changes, under ecologically-valid situations. It is particularly challenging because the majority of traditional physiological measurements require animal participants to wear electrodes and head/body restraints in a laboratory. Recent advances in infrared thermography (IRT), and its use in measuring changes in animals' skin-temperature, offer suitable solutions for these challenges. This article reviews a growing body of research employing IRT in the study of animal emotions and identify both merits and shortcomings of IRT which need to be considered when designing experiments and observations. Also, we introduce our recent efforts to facilitate the use of IRT for the study of large-body animals, such as chimpanzees. Finally, we illustrate some of the critical future directions of IRT for the study of nonhuman animals. In conclusion, the study of animal emotion is more possible than ever before with this novel technology.