Experimental and theoretical results are presented on the spectroscopy of transition states and pre-reactive van der Waals wells using negative ion photodetachment. Several benchmark reactions are discussed, including the F + H-2, OH + H-2, and F + OH reactions, as well as the isomerization of cyclo-octatetraene. Photoelectron spectra of clustered transtion state precursor anions are presented, which examine the effects of solvation on anion structure and transition state dynamics. Finally, new experiments on the photodetachment of ClH2- are discussed in which the Cl . H-2 van der Waals well is probed.