The lowest electronic states of boron monoiodide, BI, and its ions BI +/- have been theoretically studied by the multireference configuration interaction technique employing basis sets of quadruple and quintuple-zeta quality. Scalar relativistic effects and spin-orbit coupling are taken into account as well. For all states we report potential energy curves, binding energies, and spectroscopic constants. Some quantities such as electron affinity, ionization potential, and dipole moment of BI are evaluated for the first time. The nature of the bonding in the systems under scrutiny is also discussed in some detail. (C) 2017 Elsevier B.V. All rights reserved.