Inspired by the progress in the theory of dynamical systems, a great number of investigations has in the recent years been carried out to clarify the mechanisms of transition in fluid systems. These have in general focused on classical configurations of fluid flow, such as for example Rayleigh-Benard convection (e.g. Gollub & Benson [1] and Curry et.al. [2]) and rotating Couette flow (e.g. Fenstermacher et.al. [3] and Iooss [4]) and have both experimentally and numerically revealed that the transition process is connected with a rich variety of flow phenomena. A review of some of these observations and the theoretical formations they have resulted in can be found in e.g. Swinney [5], Berge, Pomeau & Vidal [6] and Eckmann & Ruelle [7]