This paper was first presented at a workshop arranged by the Netherlands Institute of Navigation on 5 November 1999 at the Delft University of Technology, The Netherlands.

The development and introduction of GPS in the early Eighties has led to an exponential growth in military and civilian applications. Worldwide, GPS is becoming a cornerstone in applications of transport, (offshore) survey, (precision) agriculture, network timing, military operations and many other applications. And yet, for a number of applications, GPS as sole-means or augmented – has some deficiencies, and its performance does not satisfy the user's requirements. Some of these deficiencies will be discussed in this paper. A number of maritime operations will be mentioned where (D)GPS as sole-means is considered by the author as unsafe navigational practice. Development and implementation of integrated navigation receivers using multiple navigation-signal sensors ((D)Galileo, (D)GPS, Eurofix, DR) using receiver autonomous integrity monitoring (RAIM) could solve the majority of the deficiencies of these systems in their stand-alone state.