Revolutionary ultra-high temperature, high mechanical loading capable, oxidation resistant, durable ceramic coatings and light-weight fiber-reinforced Ceramic Matrix Composite (CMC) systems are crucial to increase efficiency and performance of aerospace propulsion systems as well as for hypersonic and planetary entry systems. The current state-of-the-art materials include ceramic matrix composites (CMCs) and C/C composites with application temperature on the order of 2200-3000°F (1204-1650°C). A recent discovery through an ab initio molecular dynamics calculations and electronic structure modeling has identified a new hafnium-nitrogen- carbon alloy (Hf-27at%C-20at%N, or HfC0.27N0.2), which would have a melting point of more than 4400 K (7460°F, or 4127°C) . This material temperature capability is at least 200 K higher than the highest melting point ever recorded experimentally rocksalt compounds, or other cubic and hexagonal structured compounds (e.g., HfC and Ta4HfC5; hafnium or zirconium borides). This creates a new opportunity for exploring next generation Ultra-High Temperature Ceramic and Coating (UHTCC) materials for extreme environment applications with the potential for significantly increasing the temperature capability and durability beyond the current state-of-the-art CMCs. The objective of the proposed effort is to evaluate the potential of UHTCC materials based on Hf-N-C system as the next generation of high temperature material, and developing its capabilities for potential high temperature multi-functional applications. In this proposed research, we will develop fabrication technologies for processing UHTCC using HfCN based ceramics. The HfCN composition will be optimized for temperature stability, strength and oxidation resistance by evaluating the effect of various dopants (including silicon, rare earth elements, and tantalum), and in some cases (such as using for coatings or coating bond coat), with controlled oxygen content. We will also study these alloying and dopants for achieving tunable thermal and electrical conductivity for this UHTCC material. A key aspect of the proposed effort is to validate the ab-initio molecular dynamics models based on careful property measurements (such as interfacial toughness, thermodynamic properties). The down-selected compositions will then be used for processing multifunctional ceramic matrix composites reinforced with carbon nanotubes and nanofibers. We will incorporate high performance, aligned carbon nanotubes or nanofibers to develop a high thermal and electrical conductivity, high temperature ceramic matrix composites. Coatings will be developed for enhancing the durability of HfCN composites using NASA (Hf,Ta)RESiCN and other composition nano-composites, with ultra-low thermal conductivity for high temperature capability and thermal protection functions. The goal is to develop and demonstrate the potential of a light-weight UHTCC with 1500°F temperature improvements (achieving a 4500°F material), and also with tunable electrical conductivity (10-10 to 106 S·m-1) and thermal conductivity (range up to 0.1 to 100 W/m-K) in the system.