Focus of our research is to establish novel spectroscopic methods in the infrared (IR) spectral range, which resolve transient structures of molecular systems and the energy flow through them on very fast femtosecond timescales. IR spectroscopy analyzes nuclear motions of molecular systems and hence directly those degrees of freedom, which are relevant for conformational changes of bio-macromolecules. A large variety of questions is addressed, ranging from complex problems such as protein folding, energy transport in biomolecules, to elementary structural processes in liquids like water and IR-driven "photochemistry".