Considerable uncertainty has surrounded the occurrence of tetrahedrally coordinated Al and B at the T site in tourmaline. Although previously detected in several tourmaline specimens, the frequency of these substitutions in nature, as well as the extent to which they occur in the tourmaline structure, is not known. Using B-11 and Al-27 MAS NMR spectroscopy, we have investigated the presence of B and Al at the T site in 50 inclusion-free tourmaline specimens of low transition-metal content and different species (elbaite, "fluor-elbaite," liddicoatite, dravite, uvite, olenite, and magnesiofoitite) from different localities worldwide. Chemical shifts of B-|4| and B-|3| in B-11 spectra, and Al-|4| and Al-|6| in Al-27 spectra, are well resolved, allowing detection of even small amounts of T-site constituents. In the observed spectra, B-|4| and B-|3| peaks are located at 0 and 18-20 ppm, respectively, with the greatest intensity corresponding to B-|3|(=3 apfu). In Al-27 spectra, Al-|4| and Al-|6| bands are located at 68-72 and 0 ppm, respectively, with the greater intensity corresponding to Al-|6|. However, inadequate separation of Al-Y and Al-Z precludes resolution of these two bands. Simulation of B-11 MAS NMR spectra shows that tetrahedrally and trigonally coordinated B can be readily distinguished at 14.1 T and that a B-|4| content of 0.0-0.5 apfu is common in tourmaline containing low amounts of paramagnetic species Al-27 MAS NMR spectra show that Al is also common constituent of the the T site in tourmaline. Determination of Al-|4| content by peak-area integration commonly shows values of 0.0-0.5 apfu. Furthermore, the chemical shift of the Al-27 tetrahedral peak is sensitive to local order at the adjacent Y and Z octahedra, where Al-|4|-Mg-Y(3) and Al-|4|-(Y)(Al,Li)(3) arrangements result in peaks located at similar to 65 and similar to 75 ppm, respectively. Both B-11 MAS NMR and Al-27 MAS NMR spectra show peak broadening as a function of transition-metal content (i.e., Mn2+ + Fe2+ = 0.01-0.30 apfu) in the host tourmaline. In B-11 spectra, broadening and loss of intensity of the B-|3| signal ultimately obscures the signal corresponding to B-|4|, increasing the limit of detection of B-|4| in tourmaline. Our results clearly show that all combinations of Si, Al, and B: T = (Al, Si)(6), T = (B, Si)(6), T = (Al, B, Si)(6), and T = Si-6 apfu, are common in natural tourmalines.