Recently completed design studies for launch vehicle-orbiter space transportation systems have indicated that the payload weight fractions are extremely small. These studies have also identified the vehicle structures and thermal protection systems as areas of high weight-savings potential, since their combined weights may be equal to or greater than the payloads. Thermal protection systems based on rigidized and reusable ceramic insulation materials and on reinforced oxidation-resistant or inhibited carbon-carbon composites offer potential for greatly increasing the payload weight fractions. These types of materials are now undergoing extensive development. It is the purpose of this paper to describe their properties and characteristics, to summarize the progress being made in optimizing their properties and/or uniformity and reliability for shuttle vehicle applications, to present some prototype thermal protection system panel designs utilizing these materials, and to make cost and weight comparisons with other candidate systems.