Thermosensitive liquid crystals (TLC), cholesteric or chiral-nematic, have been successfully used in recent years in non-intrusive heat transfer studies. TLC have been extensively applied to the qualitative visualization of entire steady state or transient temperature fields on solid surfaces. Another group of researchers have concentrated on both perfecting the qualitative and quantitative techniques for using TLC, and applying it to temperature measurements. The main preoccupation has been the improvement of precision in the quantitative measurement of the hue, the elimination of the human vision subjectivity in the process of hue-temperature assignment and partial or full automation of the process. Most recently efforts have been under way to extend the use of liquid crystals to non-intrusive temperature measurements in fluids.