Detonation nanodiamond is a fascinating material produced in >20 t quantities annually, consisting of 5-nm diameter carbon particles. Many structural models show a partially aromatic particle surface layer, but 13C NMR documents ≤ 1% of aromatic carbons in pristine purified detonation nanodiamond. Instead, the surface is found to be covered by C-H, C-OH, and C=O moieties. The 12-14% surface carbons (i.e. with bonds to ≤3 carbons) expected for a bulk-terminated diamond particle are thus accounted for. NMR has also revealed a nonaromatic shell and provided the first estimate of the depth of the unpaired electrons from the particle surface. [JACS, 2009; J. Chem. Phys. C, 2014 & 2015]