The electronic structure and conformational properties of vinylphosphonic acid, vinylphosphoryl dichloride, and vinylphosphine oxide have been studied by ab initio quantum mechanical methods. Furthermore, the vinylphosphonic acid has been studied experimentally by means of C-13 NMR and ultraviolet spectroscopy. This compound has been synthesized by a modification of the McKenna hydrolysis reaction, improving significantly the yield. The ab initio calculations have been performed with different basis sets, including correlation energy at the MP2/6-31G* level. Topological analysis of charge density has also been carried out. Two conformers, s-cis and s-trans-gauche, have been determined for the internal rotation around the C-P bond, with low rotational barriers. Two transition structures, s-cis-gauche and s-trans, have been located. A partially polarized strong triple bond for the phosphoryl group has been found. A weak pi conjugation has been detected in the C=C/P=O system. The chemical shifts and absorption coefficients determined experimentally are in agreement with the electronic structure and conformational properties calculated by ab initio methods.