The focus of this Special Issue is on Biomedical Optical sensors. Optical sensing technologies have been widely adopted in the field of biomedical engineering for clinical and consumer applications as well as for research purposes. Tissue optics and the optical properties of various biocompatible materials and biological substances is of vast interest in medicine. Optical monitoring and analysis not only provide a powerful fingerprinting technique for various biological substances, but also provides a non-invasive tool for physiological monitoring. Continual developments and advancements in optical measuring techniques, as well as novel methods of analyses, including artificial intelligence (AI) and machine learning, are opening up new possibilities in biomedical sensing that extend beyond applications related to physiological health to include mental health monitoring, drug delivery and tracking, compliance monitoring, and personal wearable technologies.