Robust software for reconstructing a surface from scattered data has been implemented in an interactive system with graphical facilities and with highly modular machine-independent structure. Particular attention is paid to the mathematical capabilities of the system, which consist of a wide range of numerical methods for constructing a smooth bivariate function F(x, y) that approximates or interpolates certain prescribed values fk at the points (xk, yk), 1, . . ., N. These points must be distinct and noncolinear. Since this is a typical laboratory computer problem, the system has been designed for a minicomputer, and the need for both machine and operating system independence has been taken into account.