Analyses of B-11, C-13, and H-2 NMR spectra of solid hexamethylborazine, I, provide conclusive evidence for rapid in-plane jumps of the borazine ring at room temperature. Boron-11 NMR spectra of magic-angle spinning (MAS) samples, acquired at low (4.7 T), moderate (9.4 T), and high (18.8 T) external applied magnetic field strengths, have been simulated to yield the B-11 nuclear quadrupolar coupling constant (C-Q), asymmetry parameter, and isotropic chemical shift; their values at 298 K are 2.98 +/- 0.03 MHz, 0.01 +/- 0.01, and 36.0 +/- 0.4 ppm, respectively. Simulations of C-13 Cp/MAS NMR spectra provide the carbon-boron isotropic indirect spin-spin coupling constant, J(iso), the sign of C-Q(B-11), the relative orientations of the boron electric field gradient (EFG) and the C-13- B-11 dipolar coupling tensors, and the motionally averaged C-13- B-11 dipolar coupling constant. Variable-temperature H-2 NMR spectra of a partially deuterated sample of I indicate that the in-plane jumps of the borazine ring are slow with respect to C-Q(H-2)(-1) (i.e., tau(jump) greater than or equal to 10(-4) s) at temperatures less than 130 K. Over the temperature range 180 to 128 K, H-2 NMR line shape analysis yields an activation energy of 30.1 +/- 1.5 kJ mol(-1) for the in-plane jumps of the borazine ring. Although a precise experimental determination of boron chemical shift anisotropy was impeded by intramolecular and intermolecular boron-boron dipolar interactions and heteronuclear nitrogen-boron dipolar interactions, simulations of high-field B-11 NMR spectra of a stationary sample of I suggest a value of 55 +/-15 ppm for the motionally averaged span of the chemical shift tensor. Lastly, high-level ab initio and density functional theory calculations provide values of the boron EFG tensor and the boron and nitrogen magnetic shielding tensors for a rigid molecule of I.