Traditional audio editing tools do not facilitate the task of separating a single mixture recording (e.g. pop song) into its respective sources (e.g. drums, vocal, etc.). Such ability, however, would be very useful for a wide variety of audio applications such as music remixing, audio denoising, and audio-based forensics. To address this issue, we present ISSE–an interactive source separation editor. ISSE is a new open-source, freely available, and cross-platform audio editing tool that enables a user to perform source separation by painting on time-frequency visualizations of sound, resulting in an interactive machine learning system. The system brings to life our previously proposed interaction paradigm and separation algorithm that learns from user-feedback to perform separation. For evaluation, we conducted user studies and compared results between inexperienced and expert users. For a variety of real-world tasks, we found that inexperienced users can achieve good separation quality with minimal instruction and expert users can achieve state-of-the-art separation quality.