The P_spin/P_orb (Corbet’s) diagram for a large sample of HMXBs. “Classical” HMXBs are fed through localised Roche-lobe overflow and have very short spin periods. Be/X-ray binaries show a moderately strong correlation between their orbital and spin periods (Corbet 1984). Wind-fed systems have long spin periods, uncorrelated to their orbital period. The position of IGR J00370+6122 is marked by a cross.