Long-ranged correlations in a fluid close to its critical point lead to clearly identifiable effective forces on confining walls. The corresponding universal scaling functions are discussed for different boundary conditions and geometries. The theoretical predictions are compared with high precision experimental data for He4 and He3/He4 wetting films near the superfluid phase transition as well with synchrotron scattering data from classical binary liquid mixtures. Applications for colloidal suspensions are discussed.