We report spectroscopic observations on B atoms isolated in cryogenic parahydrogen (pH(2)), normal deuterium (nD(2)), Ne, Ar, Kr, and Xe matrices, and of B-2 molecules in Ne, Ar, Kr, and Xe matrices. The 2s(2)3s(S-2)<-- 2s(2)2p(P-2) B atom Rydberg absorption suffers large gas-to-matrix blue shifts, increasing from +3000 to +7000 cm(-1) in the host sequence: Xe < Kr < Ar approximate to Ne approximate to nD(2)approximate to pH(2). Much smaller shifts are observed for the 2s2p(2)(D-2)<--2s(2)2p(P-2) B atom core-to-valence transition. We assign pairs of absorption peaks spaced by approximate to 10 nm in the 315-355 nm region to the B-2 (A (3)Sigma (-)(u)<--X (3)Sigma (-)(g)) Douglas-Herzberg transition. We assign a much weaker progression in the 260-300 nm region to the B-2 (2)(3)Pi (u)<--X (3)Sigma (-)(g) transition. We report a novel progression of strong peaks in the 180-200 nm region which we suspect may be due to B-2 molecules, but which remains unassigned. Ultraviolet (UV) absorption spectra of B/pH(2) solids show two strong peaks at 216.6 and 208.9 nm, which we assign to the matrix perturbed 2s(2)3s(S-2)<-- 2s(2)2p(P-2) and 2s2p(2)(D-2)<-- 2s(2)2p(P-2) B atom absorptions, respectively. This assignment is supported by quantum path integral simulations of B/pH(2) solids reported in the following article in this journal [J. R. Krumrine, S. Jang, G. A. Voth, and M. H. Alexander, J. Chem. Phys. 113, 9079 (2000)]. Laser induced fluorescence emission spectra of B/pH(2) solids show a single line at 249.6 nm, coincident with the gas phase wavelength of the 2s(2)3s(S-2)--> 2s(2)2p(P-2) B atom emission. The UV laser irradiation results in photobleaching of the B atom emission and absorptions, accompanied by the formation of B2H6. [S0021-9606(00)00641-3].