The Music Affect Data Collection mobile application is a crowdsourcing solution to the problem of collecting emotional response data for a wide variety of music from a large sample of individuals. The app allows any user to listen to a song of their choosing through Spotify and report their emotional response to that song via a standardized valence-arousal affect model. This anonymized response data is then sent to a cloud database, where it is stored along with other crowdsourced responses for later analysis. The data produced by this app could be used as a model for automatically building mood-based playlists, refining recommendation algorithms, or identifying ideal songs for unique scenarios, among many other applications.