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Bacterial communities are able to form complex and three-dimensional biofilm structures. Biofilm formation is an ancient and integral component of the prokaryotic life cycle and a key factor for survival in diverse niches. In biofilms, bacterial lifestyle changes from free-floating cells to sessile cells. Presence in biofilms gives new traits to bacteria, which distinguish them from free cells. The presence of bacteria in biofilms results in high resistance to antimicrobial treatments and oxygen deficiency. Biofilms are formed in response to different environmental signals and many genes are involved in their production. Biofilms can be problematic in fluid transfer pipelines, on medical devices, as well as implants in the patients’ bodies. However, they can be applied for useful purposes such as treating industrial and agricultural wastewater, bioremediation of heavy metals and in air pollution biofilter systems. The potential of forming biofilms in pathogenic bacteria is an advantage for their survival in unfavorable conditions, and cause a lot of problems in their removal as the bacteria show more resistant to antibiotics and chemical pesticides in biofilms compared with free living cells. The ability to form biofilms in plant-beneficial rhizobacteria used for plant disease biocontrol, plant growth promotion and the improvement of agricultural products quality is an important advantage especially in their mass production and commercializing process. Considering the importance of bacterial biofilms in human life, this paper evaluated the importance of biofilms from different aspects.