Building on the successes of gas phase molecular spectroscopy of small molecules, we are pushing towards ever larger and more complex target systems by using electrospray ionization to prepare complex molecules from solutions. Mass selection allows us to prepare our target species without the influence of any unwanted chemical environment. The use of cryogenic ion traps enables us to add a well-controlled number of solvent molecules and to control the temperature of our target ions. We use spectroscopy from the far-infrared to the near-ultraviolet to probe the vibrational and electronic properties of molecules and clusters. This approach not only yields high-quality experimental results on complex chemical species, it also makes direct comparison with quantum chemical calculations possible, and our experimental results can serve as benchmarks for the quantum chemical treatment of complex molecular species.