We have investigated the switching and response mechanism of the in-plane switching (IFS) mode which is a novel technique for wide viewing-angle liquid crystal displays. In the IFS mode, an in-plane electric field is applied to the liquid crystals along the direction parallel to the plane of the substrates. First, it was made clear that it was the electric field. and not the voltage that drove the liquid crystals in the IFS mode. An inversely proportional relationship between the threshold voltage and the cell gap was found to hold. Second, the relaxation time of the liquid crystals when removing the electric field was described as a proportional relationship to the square of cell gap. A thinner cell gap also proved to be effective to obtain fast response time in the IFS mode. In contrast, the electric field strength governed the switching-on time when applying the in-plane electric field.