1 Temperature in Biological Species1.1 Temperature in Our Life1.2 Body Temperature1.3 Effects of Environmental Temperature on Biological Function1.4 Molecules Associated with Biological Responses to Environmental Temperature2 Development of Fluorescent Molecular Thermometers2.1 Physical Chemistry of Fluorescence2.2 Fluorescent Molecular Thermometers2.2.1 Small Organic compounds involving intersystem crossing2.2.2 Small Organic Compounds Involving Conformational Change2.2.2 Organometallic Complexes2.2.3 Excimers and Exciplex2.2.4 Host-Guest Complexes2.2.5 Thermoresponsive Macromolecules2.2.6 Inorganic Materials2.2.7 Others3 Intracellular Thermometry with Fluorescent Molecular Thermometers3.1 Early Attempts for Cellular Thermometry 3.2 Introduction of Fluorescent Molecular Thermometers into a Living Cell 3.3 Cytotoxicity Assessment3.4 Practice of Intracellular Thermometry with Fluorescent Molecular Thermometers3.5 Intracellular Thermometry with Organelle-targeted Fluorescent Molecular Thermometers3.6 Intracellular Thermometry of Brown Adipocytes3.7 Application of Intracellular Thermometry in Various Biological Fields4 Cellular Thermometry Based on Non-fluorometric Principles4.1 Infrared Thermometry 4.2 Photoacoustic Thermometry 4.3 Raman Thermometry 4.4 Use of Transmission Spectroscopy 4.5 Thermocouples4.6 Resonant Thermal Sensors4.7 Bimaterial Microcantilevers4.8 Thermistors5 Reliability of Intracellular Thermometry with Fluorescent Molecular Thermometers5.1 Validity of a Calibration Curve 5.2 Possible Artifacts in Thermometry of Biological Samples5.3 Difference between Experimentally Observed and Theoretically Calculated Intracellular Temperature Variation6 The Future of Intracellular Thermometry6.1 In vivo Thermometry6.2 Thermal Medicine6.3 Thermal Signaling6.4 Absolute Determination of Intracellular Temperature6.5 Simultaneous Measurement of Multiple Parameters6.6 Intracellular Thermometry of Plant CellsAppendixA.1 Review and account items on fluorescent molecular thermometersA.2 Comprehensive collection of fluorescent polymeric thermometers based on the combination of a thermoresponsive polymer and an environment-sensitive fluorophoreA.3 Comprehensive collection of fluorescent nanogel thermometers based on the combination of a thermoresponsive polymer and an environment-sensitive fluorophoreA.4 Non-covalent mixtures of a thermoresponsive polymer and an environment-sensitive fluorophoreA.5 Fluorescent logic gates based on the combination of a thermoresponsive polymer and an environment-sensitive fluorophoreA.6 Fluorescent inorganic thermometers