The rise of antibiotic resistant bacteria threatens the existing status quo of successful treatment of infectious diseases, leading to substantial personal and economic losses. Wastewater, carrying antibiotic resistant microorganisms from fecal origin, is an important route for disseminating anthropogenic-related resistant bacteria to natural ecosystems. Wastewater treatment plants (WWTPs), collecting and treating sewage, comprise an opportunity to mitigate such dissemination. However, because of their intrinsic characteristics, namely constant nutrient inputs, presence of selectors in sewage (i.e., antibiotics), and high bacterial densities within the biological treatment, these facilities have been postulated as environments selecting for antibiotic resistant bacteria and fostering horizontal exchange of antibiotic resistance genes (ARGs). Unravelling the ecology of antibiotic resistant determinants in WWTPs is essential to identify which stages or technologies are critical for their proliferation or removal and pinpoint possible additional or alternative intervention strategies. This thesis aims to contribute to such a quest with a multidimensional approach. The work presented here involves extensive field studies combined with qPCR measurements and statistical analysis to assess how WWTPs affect antibiotic resistant determinants. In addition, culture and molecular assays are used to investigate the conjugal exchange of plasmid-borne antibiotic resistance in wastewater environments.