Nearly-single-phase La 3 Ni 2 B 2 N 3Ϫ␦ prepared by arc melting and subsequent annealing at 1100°C is characterized by x-ray powder techniques, electron microprobe analysis, and high-resolution electron microscopy. A standardized set is provided for the crystallographic parameters, and structural chemistry is described from the point of view of nonmetal-nonmetal interactions as well as of the metal coordination around the nonmetal atoms. The superconducting properties of La 3 Ni 2 B 2 N 3Ϫ␦ are studied by means of resistivity, magnetization, and heat capacity measurements. The obtained critical fields 0 H c (0)ϭ0.16 T, 0 H c1 (0)ϭ13(2) mT, and 0 H c2 (0)ϭ7.5(5) T classify La 3 Ni 2 B 2 N 3Ϫ␦ as a hard type-II superconductor with a Ginzburg-Landau parameter ϭ33(2), a coherence length 0 ϭ7.0(5) nm, and a penetration depth (0) of about 210 nm. The pressure dependence of T c with dT c /dpϭϪ130 mK/kbar is found to be one order of magnitude larger than for RNi 2 B 2 C (RϭY, Lu͒. Since the deviations of the thermodynamic ratios as ⌬C/␥T c , ␥T c 2 /H c 2 (0),T c , and ⌬(0)/k B T c from their BCS values are rather small, La 3 Ni 2 B 2 N 3Ϫ␦ is characterized as a phonon-mediated weak-to medium-coupling BCS superconductor.