Microorganisms can degrade numerous organic pollutants owing to their metabolic machinery and to their capacity to adapt to inhospitable environments. Thus, microorganisms are major players in site remediation. However, their efficiency depends on many factors, including the chemical nature and the concentration of pollutants, their availability to microorganisms, and the physicochemical characteristics of the environment. The capacity of a microbial population to degrade pollutants within an environmental matrix can be enhanced either by stimulation of the indigenous microorganisms by addition of nutrients and/or electron acceptors (biostimulation) or by the introduction of specific microorganisms to the local population (bioaugmentation). These strategies and their variants are used for ex-situ and in situ biotreatment of contaminated sediments. Such interventions must apply the biocatalytic capacities of the microbial populations to the targeted chemical pollutants using appropriate bioreactor design and process monitoring. The presentation will discuss examples of successful bioremediation studies on contaminated sediments and will underline the real potentialities and limitations of such remediation technologies.