The use of light for scientific investigation in biomedical research and non-invasive diagnostics has become increasingly important and popular thanks to high sensitivity, minimum perturbation to living organisms, functionality and affordable cost of optical instruments enabled by recent advances in both photonic and electronic technologies. This course is designed to cover the principles, concepts, practical implementations and applications of optical spectroscopy and imaging techniques that are commonly used for biomedical sensing and diagnosis. The first part of the course introduces absorption, fluorescence, infrared, elastic scattering and Raman scattering spectroscopies. The second part of the course introduces various optical imaging techniques including conventional light microscopy techniques (phase contrast, darkfield, polarization, differential interference contrast, structured illumination), confocal microscopy, optical coherence tomography, multiphoton microscopy, quantitative phase microscopy and super-resolution imaging. Recent applications of various optical techniques in medical diagnostics will also be reviewed.