Introduction. Turbulence transition in pipe flow: 125th anniversary of the publication of Reynolds' paper

The 125th anniversary of Osborne Reynolds' seminal publication on the transition to turbulence in pipe flow offers an opportunity to survey our understanding of the nature of the transition. Dynamical systems concepts, computational methods and dedicated experiments have helped to elucidate some of Reynolds' observations and to extract new quantitative characteristics of the transition. This introduction summarizes some of the developments and indicates how the various papers in this volume contribute to an improved understanding of Reynolds' observations.