  We report a $30~\mathrm{ks}$ $Chandra$ ACIS-S survey of the globular cluster
M3. Sixteen X-ray sources were detected within the half-light radius ($2.3'$)
with $L_X \gtrsim 2.3 \times 10^{31}~\mathrm{erg~s^{-1}}$. We used
$Hubble~Space~Telescope$ WFC3/UVIS and ACS/WFC images to find 10 plausible
optical/UV counterparts. We fit the spectral energy distribution of the known
cataclysmic variable 1E1339.8+2837 with a blue ($T_\mathrm{eff} =
2.10^{+1.96}_{-0.58}\times 10^4~\mathrm{K}$, 90% conf.) spectral component from
an accretion disc, plus a red component ($T_\mathrm{eff} =
3.75_{-0.15}^{+1.05}\times 10^3~\mathrm{K}$) potentially from a subgiant donor.
The second brightest source (CX2) has a soft blackbody-like spectrum suggesting
a quiescent low-mass X-ray binary (qLMXB) containing a neutron star. Six new
counterparts have obvious UV and/or blue excesses, suggesting a cataclysmic
variable (CV) or background active galactic nucleus (AGN) nature. Two (CX6 and
CX8) have proper motions indicating cluster membership, suggesting a CV nature.
CX6 is blue in UV filters but red in V-I, which is difficult to interpret. Two
CV candidates, CX7 and CX13, show blue excesses in B-V colour but were not
detected in the UV. The other two CV candidates were only detected in the two
UV bands ($\mathrm{UV_{275}}$ and $\mathrm{NUV_{336}}$), so do not have proper
motion measurements, and may well be AGNs. One $Chandra$ source can be
confidently identified with a red straggler (a star redward of the giant
branch). The observed X-ray source population of M3 appears consistent with its
predicted stellar interaction rate.
