As ocean waves shoal and approach the shoreline, they peak and finally break, usually as either plunging or spilling breaker types. This study applies the theory of wave propagation in water of gradually varying depth, as developed by Biesel (1952), to determine the dependence of breaker type on the beach slope tangent s and on the deep water wave steepness H∞/L∞, the ratio of the deep water wave height H∞ to the deep water wave length L∞. By representing the fluid motion at the surface in Lagrangian coordinates, a graph (Figure 7) is developed for the breaker type on the basis of 21 combinations of s and H∞/L∞. A comparison with laboratory wave tank data on breaker types shows good agreement with this graph based entirely on theory. The steepening of the shoaling wave profile on the shoreward wave face leads to the occurrence of a vertical surface. The first appearance of such a vertical surface provides a natural breaking criterion compatible with experimental usage. On the basis of this breaking criterion the dimensionless ratios Hb/H∞ and Hb/hb, where Hb is the breaker height and hb the depth at breaking, are theoretically evaluated. The well-known dependence of Hb/H∞ on H∞/L∞ is also correctly demonstrated by the theoretical approach.