In contrast to the narrow fan of clinical Computed Tomography (CT) scanners, Cone Beam scanners irradiate a much larger proportion of the object, which causes additional X-ray scattering. The most obvious scatter artefact is that the middle area of the object becomes darker than the outer area, as the density in the middle of the object is underestimated (cupping). Methods for estimating scatter were investigated that can be applied to each single projection without requiring a preliminary reconstruction. Scatter reduction by the Uniform Scatter Fraction method was implemented in the Varian CBCT software version 2.0. This scatter correction method is recommended for full fan scans using air norm. However, this method did not sufficiently correct artefacts in half fan scans and was not sufficiently robust if used in combination with a Single Norm. Therefore, a physical scatter model was developed that estimates scatter for each projection using the attenuation profile of the object. This model relied on laboratory experiments in which scatter kernels were measured for Plexiglas plates of varying thicknesses. Preliminary results suggest that this kernel model may solve the shortcomings of the Uniform Scatter Fraction model.