The problem of the initial diffraction of a planar shock wave moving along the front surface of a wedge, cylinder, and sphere is solved analytically for three cases when the fluid around the body is a gas, liquid, and condensed matter, and when the reflection pattern is regular shock reflection. The conservation equations of mass, momentum, and energy are solved across the incident and reflected shocks at the reflection point moving along the body surface, using the equation of state p=ρRT for gases, Tait’s equation of state for liquids, and D=su+a for condensed matter. The monotonic increase in the reflected shock pressure along the front surface of cylinders and spheres during regular shock reflection in liquids and condensed matter is unexpectedly different from well-known results for gases in which the reflected pressure decreases from the stagnation point to a minimum farther along the body.