The crosslinking of poly(N-vinylcarbazole) PVK resulting from UV irradiation (λ > 300 nm) was studied by combining various techniques including infrared spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), swelling ratio, positron annihilation spectroscopy (PAS) and thermoporosimetry. The results obtained from all of these techniques were correlated and allowed a complete monitoring of the crosslinking during irradiation, from the creation of the first crosslinks to the formation and densification of the three-dimensional network. From SEC analysis and determination of swelling ratios, it was demonstrated that crosslinking was the predominant mechanism during the first stages of irradiation. PAS and DSC analyses revealed a good correlation between variations of free volume and increase of glass transition (Tg) of the bulk material. In addition, the development of the polymer architecture shown by the growth of Tg was nicely correlated with the modifications of the chemical structure observed by infrared analysis. Thermoporosimetry allowed the determination of the mesh size distributions within the polymer for the longest irradiation times. Numerical relationships were established and their validity was checked.