Singing, the vocal production of musical tones, is one of the most important elements of music. Addressing the needs of real-world applications, the study of technologies related to singing voices has become an increasingly active area of research. In this paper, we provide a comprehensive overview of the recent developments in the field of singing information processing, specifically in the topics of singing skill evaluation, singing voice synthesis, singing voice separation, and lyrics synchronization and transcription. We will especially focus on deep learning approaches including modern representation learning techniques for singing voices. We will also provide an overview of contributions in public datasets for singing voice research.