The aim of this work is to study the betaine calcium chloride dihydrate (BCCD) lattice dynamics by neutrons inelastic and coherent scattering. In the first part are summarized the main properties of the BCCD as they are determined in some previous experimental works. It has been more particularly emphasized on the structural and dynamical properties of this compound. The theoretical concepts used in incommensurate dielectric materials physics are given in the second part. They are at first introduced generally and then applied to BCCD. In the third part is described the experimental method used in this work : the neutrons inelastic scattering. The experimental results on the BCCD normal phase dynamics are then presented. These results and their interpretation allow to build up a semi-microscopic model introduced in the fifth part. The incommensurate lattice dynamics (at 20 K under the transition temperature towards the modulated phase) is studied in the last part. It has been shown that new aspects in relation to the previous works appear in BCCD. (O.L.). 121 refs., 25 figs., 5 tabs.