The elastic constants of pyrolytic graphite which has been highly ordered by annealing under compressive stress have been determined by ultrasonic, sonic resonance, and static test methods. Ultrasonic tests yielded the elastic constantsc11,c12,c33,c44= 1/s44, and the stress derivative ofc33. The moduli 1/s11andc44were determined from the free flexural resonant vibrations of bars, and the shear modulusc44also was determined from the fundamental torsional resonance of the bars and from the resonance of compound torsion oscillators composed of thin graphite disks with steel end pieces. Static tension, compression, and torsion tests on the pyrolytic graphite yielded a complete set of compliances (s11,s12,s13,s33, ands44). The following self‐consistent set of elastic constants (cijin units of 1011dyn/cm2;sijin 10−11cm2/dyn) has been deduced from the results:c11= 106±2,c12= 18±2,c33= 3.65±0.10,c13= 1.5±0.5,c44= 0.018 to 0.035, 1/s11= 102±3, 1/s33= 3.65±0.10,s12= −0.0016±0.0006,s13= −0.0033±0.0008, ands66= 0.023±0.002; with the possible exception ofc44, these constants are expected to be typical of the graphite single crystal. The shear strength for shear between basal planes was found to be in the range of 90–250 g/mm2.