Using augmented sextuple zeta basis sets and internally contracted multireference configuration interaction (MRCI) wavefunctions, potential energy, electric dipole and transition moments have been computed for the X(3)Pi, a(1)Sigma(+), b(1)Pi and A(3)Sigma(-) states of BP, X(2)Sigma(+) and A(2)Pi states of BP(-) and X(4)Sigma(-) and A(4)Pi states of BP(+). From these data spectroscopic constants, radiative transition probabilities and photoelectron spectra of BP- and BP have been evaluated. The non-vanishing spin-orbit coupling elements between the four low lying triplet and singlet states of the neutral BP have also been calculated from MRCI wavefunctions. The treatment of the corresponding perturbations in the manifold of dense rovibrational states in the three lowest states would require a precise knowledge of the electronic excitation energies. Our best singlet-triplet separations (X-a) are calculated to be 2412 cm(-1) (MRCI) and 2482 cm(-1) (restricted coupled cluster with perturbative triples (RCCSD(T))) with an estimated error bound of about +/ 200 cm(-1). All three states have long radiative lifetimes with cascading among the rovibrational levels of different states. The ionization energy IE(e) of BP is calculated to be 9.22 eV (MRCI) and 9.48 eV (RCCSD(T)), the electron affinity EA(e) 2.51 eV (MRCI) and 2.74 eV (RCCSD(T)). The photoelectron spectra of BP and BP- have been obtained from the Franck-Condon factors of the MRCI potentials. For the UV spectroscopy the dipole allowed radiative transition probabilities are given for A(3)Sigma(-) <-> X(3)Pi, b(1)Pi <-> a(1)Sigma(+) of BP, A(2)Pi <-> X(2)Sigma(+) of BP and A(4)Pi <-> X(4)Sigma(-) of BP(+). The ionization energy IE(e) of B(2)P(2) of 8.71 eV and the electron affinity EA, of 2.34 eV have been calculated by the RCCSD(T)/aVQZ approach. Also the harmonic vibrational wavenumbers for the electronic ground states of the ions B(2)P(2)(+) and B(2)P(2)(-) are given.