In continuing with our work to find new pathways to bis(phosphonate) structures we report on their synthesis from tris(trimethylsilyl) phosphite and acid anhydride. This new synthesis allows a direct access to a 1‐hydroxymethylene‐1,1‐bis(phosphonic acid) functionalised by a carboxylic function on the side chain. Moreover, we describe the formation of an original cyclic bis(phosphonate) obtained from phthalic anhydride. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)