In this chapter, the contactless thermal sensors based on luminescence properties of rare earth-doped nanocrystalline phosphors are discussed. The luminescence thermometry is considered nowadays as a remote and noninvasive approach providing excellent functional parameters—high thermal sensitivity and spatial resolution, wide working temperature range and short response times. The competitive advantage of the luminescence thermometry is its applicability in specific environmental conditions like external electromagnetic field, fast-moving objects, flows and fluids of different nature. The key functional characteristics of temperature sensors are described in the chapter together with different strategies of temperature readout including variants of ratiometric approach via thermally coupled levels, Stark sublevels, spectral line position, and bandwidth and lifetime thermometry. Further progress in this direction includes stimulated market demands and industrial development of micro- and nanoelectronics, photonics, nanomedicine, micro- and nanofluidics, as well as academic interest and scientific challenge in the improvement of current intrinsic limitations. The presented analysis of emerging new directions in the field of luminescence thermometry testifies an interest in widening the working spectral range, development of multi-sensing devices based on multiple emission centers, etc. All these open fascinating prospects of luminescence thermometry in the future and development of even newer fields such as multimodal imaging with temperature monitoring, 3D temperature mapping, and temperature-supervised processes.