The initial aim of the work presented in this thesis was to examine smecticlayer compressibility with a view to improving our understanding of the stability ofintermediate phases. A natural starting point was to investigate the smectic-A phase,as it is the most basic of the smectic phases. The response of the layered structure toexternal fields is also a focus of this thesis as electric and magnetic fields enable thelayer properties to be probed.Investigations into the reorientation dynamics of smectic-A layers inmagnetic fields were performed using geometries and cell thicknesses (>50 micro metre) thatare not feasible using electric fields. Data presented in this thesis show that threedistinct reorientation mechanisms can occur, one of which is previously unreportedand bridges the gap between the previously known mechanisms. The newmechanism observed in 270 micro metre and 340 micro metre thickness cells exhibits multiple stagereorientation on a timescale between tens and hundreds of seconds.Using conventional electro-optic techniques combined with a theoreticalapproach developed by others, this thesis presents a new technique to providemeasurement of relative smectic layer compressibility of eight smectic-A liquidcrystalline materials. The method presented here combines data on cell thickness,dielectric anisotropy and the measurement of the voltage threshold of the toroidal tostripe domain transition. As expected, the experimental data indicated that materialswith shorter molecular lengths had the largest relative layer compressibility. Finally, direct measurement of smectic layer compressibility was investigated and the design of an apparatus capable of such measurements was undertaken. Preliminary results from such an apparatus are presented along with a discussion on the steps taken to develop the design.