The early history and development of thermal barrier coatings (TBC) are reviewed. The TBC as a system highlights the separate properties and interactions of the substrate, metallic bondcoat and the insulative ceramic layer. The role of density in the now-predominate 7% yttria-stabilized zirconia ceramic in thermal conductivity, particle erosion and the effects of starting powder type and morphology are discussed. The properties of typical MCrAlY bondcoats that affect oxidation life, bonding to the YSZ layer, yield strength vs. temperature, compositional effects on thermal expansion, and structures obtained by different thermal spray method are reviewed. Methods of testing TBC properties, as well as some modeling of zirconia conductivity and TBC thermal shock are mentioned.