Recent studies in the area of biological waste air treatment in biotrickling filters have addressed fundamental key issues, such as biofilm architecture, microbiology of the process culture and means to control accumulation of biomass. The results from these studies have provided a deeper insight into the fundamental mechanisms involved during biotrickling filtration. In the coming years, these and future advances should allow for the design of better reactor controls and the improvement of pollutant removal in these gas phase bioreactors. Ultimately, this should lead to a more widespread use of biotrickling filters for air pollution control.