We propose to investigate changes that occur in acetylene dicarboxylic acid dihydrate as a function of pressure. This system, for which there is a general paucity of structural data, is structurally similar to its simpler congener oxalic acid (differing only by the insertion of an acetylene group) and is known to undergo several phase changes on cooling. Oxalic acid and its hydrates possess a rich structural chemistry, including a phase change seen in the dihydrate caused by the application of pressure. By analogy, we expect these changes in acetylene dicarboxylic acid dihydrate to involve proton migration, with the possibility of the formation of hydronium ions and dicarboxylate ions, and we will account for these structural changes. From the knowledge gained from this work we will elucidate the role of proton transfer in driving polymorphic changes in the solid state.