clipsing X-ray Binary pulsars are the only interacting binaries in which the neutron star masses may be measured dynamically. There are only 10 such systems known and various issues arise when making measurements to determine their masses. The equation of state and upper limits on neutron star masses are not well constrained theoretically and, whilst neutron star masses in binary radio pulsars are consistent with the narrow range 1.35 0:04 M_sun, evidence exists that millisecond pulsars with white dwarf companions have neutron star masses >1.4 M_sun. In this talk I shall describe results of measuring neutron star masses in 6 eclipsing high mass X-ray binary pulsars over the last few years. I shall highlight some of the issues that arise and describe current efforts to pursue this programme using infrared spectroscopy of obscured sources in the Galactic plane.