Hydrodynamic stability is of fundamental importance in fluid dynamics and is a well-established subject of scientific investigation that continues to attract great interest in the fluid mechanics community. Hydrodynamic instabilities of prototypical character are, for example, the Rayleigh–Bénard, the Taylor–Couette, the Bénard–Marangoni, the Rayleigh–Taylor, and the Kelvin–Helmholtz instabilities. A fundamental understanding of various patterns of bifurcations such as identifying the most dominant mechanisms responsible for the instability threshold is also required if one is to design reliable and efficient industrial processes and applications, such as melting, mixing, crystal growth, coating, welding, flow re-attachment over wings, and others.

The collection of papers in this volume is a selection of the presentations given at the Second International Symposium on Instability and Bifurcations in Fluid Dynamics, Technical University of Denmark, 15–18 August 2006. With more than 40 invited and contributed papers the symposium gave an overview of the state-of-the art of the field including experimental, theoretical, and computational approaches to problems related to convection, effects of magnetic fields, wake flows, rotating flows, and many others. The complete program can be found at the conference website http://www2.mat.dtu.dk/BIFD2006/.

The symposium was the follow-up of a minisymposium held as a part of the `International Conference on Computational and Experimental Engineering and Sciences', 26–29 July 2004, Madeira, Portugal. We hope it will be possible to continue this series of highly successful events with a third symposium in 2008.

P Z Bar Yoseph, M Brøns, A Gelfgat and J N Sørensen
Editors