Satellite-based navigation rapidly evolved into an efficient tool extensively used in a wide variety of civilian applications covering numerous modes of transportation, communication, administration, geodesy, agriculture, and many others. The current systems globally available are the US Global Positioning System (GPS) and the conceptually very similar Russian Global Navigation Satellite System (GLONASS). Considering the worldwide applications, GPS clearly predominates over GLONASS. However, GPS and GLONASS are mainly under military control of single nations and, also critical, do not fulfill certain performance requirements of the civil users, especially in terms of safety-critical applications. Thus, augmentations to the current systems and even completely new systems are under investigation. These are usually summarized under the abbreviation Global Navigation Satellite Systems (GNSSs). The various types of GNSS are described where emphasis is put on the future US and European contributions to the second-generation GNSS, i.e., the modernized GPS and the definition of the new European Galileo system. These two systems may be characterized as "compatible competitors"—thus, one might ask for whom the bell tolls.