Very low threshold field emission from undoped microcrystalline diamond films grown by the hot filament chemical vapour deposition process (HFCVD) is reported. The effect of crystal size, methane concentration and the temperature has been studied. The microcrystalline diamond films grown using 3% methane (CH4) / hydrogen (H2) gas mixture ratio under varying deposition temperatures exhibit very low emission threshold fields. The threshold fields varied from 0.4 V/μm to 1 V/μm for an emission current density of 1 μA/cm2. A correlation between the emission characteristics and the material properties is presented. These films exhibit an emission site density of ∼104-105/cm2 at an applied field of 3 V/μm.