Antibiotics (AB) are among the most important pharmaceuticals applied in both, human and veterinarian medicine. As long as their use, concerns about an increase in resistance (ABR) of originally targeted organisms exist. Within the last few years the significance of wastewater treatment plants and the release of antibiotic resistant bacteria (ARB) or genes (ARG) by discharged effluents got into the focus of scientific research. Within a wastewater treatment plant there are two specific conditions that could induce transfer of ARGs and selection of ARBs: • Low concentrations of antibiotics that are far below a therapeutically dose and can act as selection parameter for ABR • Living or dead resistant clinically relevant bacteria that can transfer their ARGs via different means to environmental bacteria that are adapted to usual environmental conditions and therefore can transfer ARGs to the gene pool of the aquatic environment Both aspects can be demonstrated by applying the concept of the “mutant selection window” to wastewater treatment plants that implies that between a miniumum inhibitory concentration (MIC) and a higher mutant prevention concentration (MPC) there is a concentration range where an antibiotic has an effect on the selection of ARBs.The pathway of resistance back from the environment to the human is not clear now and hardly investigated. As awareness ARBs and ARGs by wastewater treatment plants is there now, engineers are about to adopt existing treatment technologies for decreasing the release and are designing new technologies that even are able to inhibit their release to the aquatic nvironment.