GEOPAC .consists of a series of subroutines to primarily process potential-field geophysical data but other types of data can also be used with the program. The package contains routines to reduce, store, process and display information in two-dimensional or three-dimensional form. Input and output formats are standardized and temporary disk storage permits data sets to be processed by several subroutines in one job step. The subroutines are link-edited in an overlay mode to form one program and they can be executed by submitting a card containing the subroutine name in the input stream.