Strong interacting scattering processes in the limit when the 
center-of-mass energy is much larger than any other scale have 
very intriguing properties: The effective degrees of freedom are 
Reggeized gluons and the scattering amplitudes have ladder structure. From 
the formal side this limit is related to integrable systems and 
linear and non-linear evolution equations. The phenomenological applications 
include processes with two large perturbative scales at hadron-hadron 
colliders and deep inelastic scattering. A brief introduction to this field 
of research will be given.