The application of ion storage rings to the study of electron-molecular ion interaction has led to an experimental breakthrough. The development since the first experiments with molecular ions in storage rings about seven years ago, which in themselves represented a big leap forward, has been striking, and was impossible to envision at the outset. The development has been driven by advances in accelerator physics, detector technology, challenging applications in astrophysics and atmospheric physics, and by a close interplay with theory. Despite the remarkable progress, many important questions remain unanswered. For example, even for someone with a good knowledge of molecular physics it may come as a surprise that it is far from understood how the simplest polyatomic moleculeH3+recombines with electrons, and it remains an experimental controversy at what rate it recombines. ©2000 American Institute of Physics.