Free radicals, weakly bound van der Waals complexes, and metal and semiconductor clusters are characterized by photodetachment of the corresponding negative ions using slow electron velocity-map imaging (SEVI), a recently developed, high-resolution (2-3 cm-1) variant of negative ion photoelectron spectroscopy. The SEVI spectrum of a negative ion yields the electron affinity of the neutral, term values for excited states accessible via one-photon detachment, and accurate vibrational frequencies for the ground and accessible excited states. The combination of high energy resolution and the simultaneous measurement of photoelectron angular distributions provides a sensitive probe of adiabatic potential energy surfaces and vibronic coupling in neutral species formed by photodetachment. The SEVI experiments are complemented by infrared studies of size-selected negative ions and clusters using the free electron laser FELIX.