Geophysical data are often subjected to a variety of selective sampling operations in order to render their interpretation easier. The filtering effects of a number of commonly employed selective sampling procedures are discussed in detail in this paper. Curves are given showing the frequency selectivity characteristics of several arithmetic sampling processes including simple averaging, successive differences, and residual curves and maps. Instrumental sampling such as geophone mixing and electric filtering is also considered. The equivalence of electric filtering to an arithmetic sampling process is pointed out and illustrated by an example. A recently developed statistical method of detecting seismic reflections is discussed as a sampling procedure, and curves are presented to show the filtering action for two special cases under restricted conditions.