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The paramagnetic resonance spectra of Mn2+ ions in glasses and compounds of the lithium borate system have been investigated at 9.1 and 35 GHz. The spectrum for the Li2O·4B2O3 compound is found to exhibit six very sharp hyperfine lines centered on g=3.3 when observation is made at X band, while at 35 GHz the center of the principal hyperfine sextet is seen to have shifted to g=2.0. This spectrum is interpreted by assuming a spin Hamiltonian containing crystal-field terms comparable to the Zeeman energy at X band. By means of a computed diagram it is determined that | D | /h=3.7 GHz and | E/D | =0.333. The same diagram is found useful in interpreting the ESR spectra of Mn2+ in lithium borate glasses. It is shown that in the glasses the manganese ions experience wide spreads of crystal fields, giving rise to fine-structure parameters ranging from near zero to 4 GHz or greater, with an apparent constraint favoring | E/D | ratios of approximately ⅓. It is concluded that many of the Mn2+ sites in the glasses are probably distorted versions of the site occupied in the Li2O·4B2O3 compound.