The need to map temperature distributions at the micrometer level in a diversity of samples is stimulating the development of thermosensitive organic fluorophores with dual emission. Their ability to provide pairs of output signals simultaneously offers the opportunity to probe temperature ratiometrically and overcome the concentration effects and optical artifacts that plague methods based on single emission. Pronounced modifications in structure with temperature are generally invoked to ensure such a ratiometric response. Indeed, conformational changes in either the excited state or the ground state can be exploited to construct thermosensitive molecular, macromolecular and supramolecular systems. Alternatively, the rapid equilibration of two fluorophores with resolved emissions can be designed around the opening and closing of heterocyclic rings to impose, once again, ratiometric response. The behavior of these thermosensitive constructs in conjunction with the fast response time, inherent sensitivity, noninvasive character and spatial resolution of fluorescence imaging permits thermometric analyses at dimensional scales that cannot be accessed with conventional thermometers.