In the past twenty years optical spectrometers have shrunk dramatically in size, giving us successively laboratory-portable, toaster-sized, instruments; cordless-drill-sized portable instruments for use in the field; and onto spectrometers the size of a computer mouse or deck of cards. The latest development in portable spectroscopy is the availability of very low-cost multispectral sensors, the size of computer chips, leading to the possibility of embedding them into consumer goods. Multispectral sensors can now not only be incorporated into ‘white goods’ like washing machines and dryers, but also into ‘fitness’ products like smart watches and sports watches, and as photonic miniaturization increases, into ‘wearables’ like smart rings, providing the user with health information. A variety of photonic components and technologies can be utilized for these miniature devices including silicon photonics and photonic integrated circuits (PICs), produced en masse using semiconductor manufacturing techniques; components from LiDAR including SPAD arrays; electronically-tunable detectors; and 'photonic’, ‘plasmonic’ and ‘computational’ devices. This course surveys technologies and applications for miniature optical spectrometers and spectroscopic sensors.