Temperature is a widely known phenomenon, which plays an extremely important role in biological systems. Its behavior on the macro-scale has been quite well investigated and understood, thanks to the availability of reliable and precise thermometers such as thermocouples and infrared cameras. However, temperature measurements on the subcellular scale present an ongoing challenge due to the absence of universal nanoscale temperature sensors. Recent work on fluorescent nanodiamonds has revealed their unique ability to measure temperature with high spatial and temporal resolution, of particular importance in the intracellular environment. This review summarizes recent progress in the field and highlights the future directions for intracellular temperature sensing using fluorescent nanodiamonds