Tuning of nonlinear optical (NLO) properties of organic chrothophores (OCs) by stereo-electronic and environmental effects has been widely documented by different experimental techniques and theoretical studies. Disentanglement and analysis of the different contributions requires, however, the -availability, of effective yet accurate quantum Mechanical, approaches for!mediom to large size systems, in their natutal environment. AS a -first -step, we have shortly reviewed the phenomenological,models used, by.experimentalists to interpret their results and shown that a quantum 3. mechanical, approach based on the density functional theory (DFT) and the polarizable continuum model,(PCM) should be able to' overcOme most, theoretical limitations allowing, at the same tirne, -the study of large systems with reasonable computational resources and the analysis Of the results in, terms of well-defined physical chemical effects, After validation of the -most suitable density functionalibasiS- set in conjunction with the PCM description = of bulk solvent effects, we have pefformed a systematic study of representative OCs, especially:cationic ones, with special reference to their fir, st order hyperpolarizability. The internal consistency of the results and their good agreement, with experiment paves the route toward integrated experimental/computational studies of NLO properties taking together physical soundness, feaSibility, reliability, and ease of interpretation.