This study is motivated by the evidence that software engineers do not sufficiently consider the emotional needs of users when designing software systems. Emotional needs can be captured as emotional requirements that represent how the user should feel when using the system. Failure to address emotional requirements hinders the adoption of systems by end users and decreases user experience, which may lead to huge costs because of the possible need to adopt a new system. Such a problem could be avoided if the emotional requirements would be explicitly elicited and represented during requirements engineering and system design. This paper applies the systematic mapping study technique for surveying and analyzing the available literature to identify the most relevant publications on emotional requirements. We identified 35 publications that address a wide spectrum of practices concerned with engineering emotional requirements. The identified publications were analyzed with respect to the application domains, instruments used for eliciting and artefacts used for representing emotional requirements, and the state of the practice in emotion-related requirements engineering. Our study encourages software engineers to consider emotional requirements during requirements engineering and system design and facilitates dealing with such requirements. To the best of the knowledge of the authors, no other similar study has been conducted on emotional requirements.