Thermal sprayed abradable seal coatings are a specially designed class of materials used to reduce gas path clearance in gas turbine engines. These coatings directly translate to lower engine fuel consumption and higher performance and are employed in virtually every commercial and military jet aircraft in operation, Abradable coatings are characterized by a friable structure of carefully selected materials. These coatings are difficult to design since they must be readily abrad able and yet resist particle impact erosion from engine ingested abrasive dust at high gas velocities. Other important criteria are temperature stability, inertness, and consistency. This paper describes the classes of abradable seal materials; the characterization of thermal sprayed abradables; current coating materials temperature, erosion, and abradability performance; and current research in thermal sprayed abradable coating materials.