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abstract: 'We have discovered a new transient low-mass X-ray binary, NGC 6440 X-2, with /ACIS, /PCA, and /XRT observations of the globular cluster NGC 6440. The discovery outburst (July 28-31, 2009) peaked at $L_X\sim1.5\times10^{36}$ , and lasted for $<$4 days above $L_X=10^{35}$ . Four other outbursts (May 29-June 4, Aug. 29-Sept. 1, Oct. 1-3, and Oct. 28-31 2009) have been observed with /PCA (identifying millisecond pulsations, Altamirano et al. 2009a) and /XRT (confirming a positional association with NGC 6440 X-2), with similar peak luminosities and decay times. Optical and infrared imaging did not detect a clear counterpart, with best limits of $V>21$, $B>22$ in quiescence from archival  imaging, $g''>22$ during the August outburst from Gemini-South GMOS imaging, and $J\gsim18.5$ and $K\gsim17$ during the July outburst from CTIO 4-m ISPI imaging. Archival  X-ray images of the core do not detect the quiescent counterpart ($L_X<1-2\times10^{31}$ ), and place a bolometric luminosity limit of $L_{NS}< 6\times10^{31}$  (one of the lowest measured) for a hydrogen atmosphere neutron star. A short  observation 10 days into quiescence found two photons at NGC 6440 X-2’s position, suggesting enhanced quiescent emission at $L_X\sim6\times10^{31}$ . NGC 6440 X-2 currently shows the shortest recurrence time ($\sim$31 days) of any 