The present invention relates to a curable rubber composition comprising an organic elastomer, a filler and at least one curing agent for the elastomer. Such curable rubber compositions are widely used in the production of cured rubber articles, such as tires, belts and hoses. The composition contains a branched silicone resin having Si-bonded hydroxyl groups or azo groups. This may lead to a reduction in the mixing energy required for processing, particularly in the energy required in the first (non-productive) mixing phase to give good dispersion of the filler in the organic elastomer. Use of the branched silicone resin can also accelerate cure (vulcanization), thus reducing the required cure time or reducing the amount of cure accelerator required.