I review the current status of studies of the X-ray sources in Galactic old open clusters .
Cataclysmic variables ( CVs ) , magnetically-active binaries ( ABs ) , and sub-subgiants ( SSGs ) dominate the X-ray emission of old open clusters .
Surprisingly , the number of ABs detected inside the half-mass radius with L _ { X } \gtrsim 1 \times 10 ^ { 30 } erg s ^ { -1 } ( 0.3–7 keV ) does not appear to scale with cluster mass .
Comparison of the numbers of CVs , ABs , and SSGs per unit mass in old open and globular clusters shows that each of these classes is under-abundant in globulars .
This suggests that dense environments suppress the frequency of even some of the hardest binaries .