Thus far, crowdsourced and interactive music have been limited, with the public only a small part of a final musical result, and often disconnected from the artist leading the project. We believe that a new “musical ecology” is needed for true creative collaboration between experts and amateurs that benefits both. For this purpose, we created a new symphony in collaboration with the entire city of Toronto. Called “A Toronto Symphony,” the work–commissioned by the Toronto Symphony Orchestra–premiered in March 2013. We designed the necessary infrastructure, a variety of web-based music composition applications, a social media framework, and real-world community-building activities to bring together an unprecedented number of people from diverse backgrounds. This process establishes a new model for creating complex collaborations between experts and everyone else.