Environmental effects on electronic states of small molecules in solid rare gases and in liquids have severe consequences on the photochemistry; examples for valence, Rydberg and ionic states as well as the connection to photochemical dry etching are treated. The repulsive interaction of Rydberg states and the solvation of valence and ionic states are related to spectroscopic properties like gas-to-matrix shifts, Stokes shifts and linewidths. Differential shifts of Rydberg and valence states are illustrated for NO in rare gas matrices and Fano-type line shapes are attributed to a coherent interaction of broad Rydberg multiphonon continua with valence zero phonon lines. For F 2 in Ne a deperturbation of ion-pair and Rydberg states is demonstrated again to originate from a differential shift. For Cl 2 the formation of additional states due to intermolecular charge transfer from the matrix to the guest molecules is observed. H 2 O serves as an example to show that repulsive surfaces are strongly modified if the character of the state changes from Rydberg type to valence type with internuclear distance. Information on the dynamics in the femtosecond time scale is derived from intensities in overtone progressions of resonance Raman spectra and it is demonstrated that the solvent induces predissociation of the B 3 o + u state of I 2 within 300 fs in CCl 4 , and within 40 fs in liquid Xe.