Our neighbouring galaxy M31 (Andromeda), located 780 kpc away, offers a unique opportunity to study the X-ray population of a galaxy similar to the Milky Way. We have concentrated our monitoring campaign on following the X-ray activity of the stellar-mass black hole candidates, XRNe (X-Ray Novae), in the central region of M31. Observations are made approximately once a month with Chandra, following up any bright outbursts with HST in order to identify the optical counterparts. Having measurements of the X-ray and optical luminosities, both in outburst and quisence, allows for the estimation of a system's orbital period. In this way we have now calculated or constrained this important parameter for 6 systems, and will have a further 6 by the end of the current Chandra cycle. With 12 orbital periods known, it will be possible to compare these values to those of the X-ray binary population in our own galaxy.