A method is presented to create smooth B-spline surfaces on basis of three-dimensional data points. The intended application is interactive shape design and shape representation with CAD workstations. This type of application allows specific assumptions to be made on the input data points, and it implies requirements in terms of speed and integration of the method with at least a graphics environment. There are no restrictions on the data locations, they need not fit into a grid and may be irregularly spaced. In an automatic process, the data are first represented by an array of B-spline curves. The parametrizations of these are harmonized as to enable approximate representation (within some tolerance) by a single B-spline surface with the smallest possible number of control points. The fitting system can also be used to represent a large amount of data points by an approximating surface, thus providing data compression.