The off-gas treatment of hydrophobic pollutants in conventional biotechnologies is typically limited by the gas-liquid mass transfer as a result of the low-concentration gradient imposed by their high partitioning coefficients. The addition of a non-aqueous-phase (NAP) with a high affinity for the gas pollutant to packed bed or suspended-growth bioreactor configurations has resulted in enhanced elimination capacities and process robustness. Despite recent research has just added more desired characteristics to the selection criteria of the optimum NAP in gas treatment applications, silicone oil continues being the most popular mass transfer vector. This technology has been successfully applied to the treatment of hexane, methane, styrene, alpha-pinene and BTEX in biofilters, biotrickling filters, stirred tank and airlift bioreactors. The maximum potential of two-phase partitioning bioreactors (TPPBs) during off-gas treatment is achieved when the microbial community is confined inside the NAP. TPPB modeling has also experienced significant advances, the most advanced platforms being able to describe the recent findings in the field. This chapter will compile and critically discuss the fundamentals and most recent breakthroughs in the field of TPPBs for gas treatment applications.