The FOPI detector has documented the investigation of the fragments and the particles produced in central heavy-ion collisions. As suggested by the name, FOPI stands for 4p, a synonym for the entire solid angle-this detector detects, identifies, and determines the momentum of all charged particles emitted in a heavy-ion reaction. The detector structure is shown schematically in Figure 1. Based on the modular combination of different subdetectors, the total assembly achieves its goal of covering the complete range of beam energies (0.1 - 2 GeV per nucleon) made available by GSI's SIS heavy ion synchrotron. The target is located within a superconducting coil, which produces a magnetic field of 0.6 Tesla. Charged particles within this field travel along curved paths before passing through the drift chambers (shown in yellow).