An antimicrobial agent kills microorganisms or inhibits their growth. Antimicrobial agents may be antibacterial, which work against bacteria; antifungal, against fungi; microbiocides, which kill microbes; or microbiostatic, growth inhibitors of microbes. Generally it is defined as disinfectants or antiseptics or antibiotics or bactericidal or bacteriostatic agent. An antimicrobial therapy is a treatment modality that attacks the microorganisms responsible for a specific disease or condition. Many bulk metals such as copper and its alloys (brasses, bronzes, cupronickel, copper-nickel-zinc, and others) are natural antimicrobial materials. Also, ions of copper, silver, mercury, lead, iron, bismuth, aluminum, zinc, and gold act as antimicrobial agents. In addition, numerous phytochemicals and synthetic compounds have been used as antimicrobial agents. After the discovery of penicillin, actinomycin, and streptomycin, medical sciences tried to use antibiotics instead of antimicrobial agents like silver. Nowadays, due to increasing drug-resistance and growing concern regarding the over-prescribing of antibiotics, the scientific community is searching for antimicrobial agents which can solve the above problems. Hence nanobiomaterials are coming up as emerging materials of the future in medical science. A thorough literature survey on nanobiomaterials used as antimicrobial agents showed that nanomaterials such as silver, gold, iron, copper, iron oxide (FeO, Fe2O3, Fe3O4), copper oxide (Cu2O, CuO), zinc oxide (ZnO), titanium dioxide (TiO2), silver oxide (Ag2O), cadmium oxide (CdO), alumina (Al2O3), nickel oxide (NiO), silica (SiO2), tin oxide (SnO2), and cadmium telluride (CdTe) quantum dots show antimicrobial activity toward various bacteria and microbes. Also, this chapter will provide a brief highlight of other nonmetallic carbon-based nanomaterials for their antimicrobial activity. Finally, this chapter will provide a brief highlight of a mechanistic approach for all. © 2016 Elsevier Inc. All rights reserved.