Electrospray ionization (ESI) is a gentle, state-of-the-art technique to introduce biomolecular ions from solution into the gas phase and into vacuum, providing a solvent- and substrate-free environment. This enables to study the molecule in a well-defined, isolated state, where only intramolecular interactions have to be considered.  The combination of an ESI source and mass spectrometry at advanced light sources such as synchrotrons and free-electron lasers allows for a novel and unique way to investigate structure and dynamics of gas-phase biomolecules. Ionization and dissociation processes dependent on photon energy and intensity will be discussed for different peptides, proteins and oligonucleotides.