We report the first results from deep ACS imaging of ten classical globular clusters in the far outer regions ( 15 \lesssim R _ { p } \lesssim 100 kpc ) of M31 .
Eight of the clusters , including two of the most remote M31 globular clusters presently known , are described for the first time .
Our F606W , F814W colour-magnitude diagrams extend \sim 3 magnitudes below the horizontal branch and clearly demonstrate that the majority of these objects are old ( \gtrsim 10 Gyr ) , metal-poor clusters .
Five have [ Fe / H ] \sim - 2.1 , while an additional four have -1.9 \lesssim [ Fe / H ] \lesssim - 1.5 .
The remaining object is more metal-rich , with [ Fe / H ] \sim - 0.70 .
Several clusters exhibit the second parameter effect .
Using aperture photometry , we estimate integrated luminosities and structural parameters for all clusters .
Many , including all four clusters with projected radii greater than 45 kpc , are compact and very luminous , with -8.9 \lesssim M _ { V } \lesssim - 8.3 .
These four outermost clusters are thus quite unlike their Milky Way counterparts , which are typically diffuse , sub-luminous ( -6.0 \lesssim M _ { V } \lesssim - 4.7 ) and more metal-rich ( -1.8 \lesssim [ Fe / H ] \lesssim - 1.3 ) .