We report the results of a comprehensive investigation of the two-color threshold photoionization of jet-cooled indole clusters. Using two-color photoionization spectroscopy, we have probed both the neutral excited levels and the ground ionic states of indole clusters containing non-polar (Ar, CH 4, CF 4, C 6H 6) and polar (H 2O, MeOH, EtOH, NH 3, N(CH 3) 3) solvent species. These studies have allowed the determination of accurate cluster ionization energies (IEs) as well as the assignment of electronic absorption features to clusters of known composition. The determination of the cluster IE, which is typically lower than that of bare indole, has allowed us to investigate the importance of charge-induced dipole and charge-dipole attractive forces in the binding of the ion-neutral clusters. In addition, we have found that the shape of the photoionization efficiency (PIE) spectra gives valuable information regarding the relative shape and/or position of the potential energy surfaces of the neutral excited and ground ionic states of the clusters. We have also identified two distinct conformational isomers of the indole-(H 2O) 1 hydrogen bonded cluster using the techniques of electronic spectroscopy, two-color threshold ionization spectroscopy and mass analysis.