The evolution of the joint distribution of wave heights and periods that results from shoaling is investigated using laboratory data obtained from experiments conducted on two (1:40 and 1:20) planar beach slopes. The data are compared to the theoretical joint distribution for wave heights and periods proposed by Longuet-Higgins (1983). For unbroken waves with d/L>≈0.1 the shapes of the observed and predicted distributions agree reasonably well. However, the predicted joint distribution given by Longuet-Higgins (1983) is displaced relative to the observed distribution. A parameterization for the observed displacement is offered. In addition, a parameterization for the variation of the spectral width parameter through the shoaling regions is also given. ¿ American Geophysical Union 1993