Bacterial membrane vesicles are nanoscale lipid bilayer biomaterials (30–250 nm), obtained from both gram-positive and gram-negative bacteria, formed through distinct biogenesis mechanisms. These non-replicating vesicles comprise lipopolysaccharides, phospholipids, peptidoglycan, membrane proteins, and cargoes such as enzymes, toxins, and nucleic acids. Bacterial membrane vesicles inherit key attributes from their parent bacteria, reflecting their membrane composition, and play critical roles in pathogenesis, quorum sensing, nutrient acquisition, intercellular communication, and immune activation. Their unique biochemical and physicochemical properties position them as promising therapeutic nanomaterials. However, variability in surface markers and composition can cause batch-to-batch inconsistencies, toxicity, off-target effects, and weak immunogenicity, limiting their efficacy and safety. To address these challenges, careful selection of cell sources and bacterial membrane vesicles engineering is essential for enhancing immune-reactive determinants, minimizing toxins, optimizing payload loading, and improving targeted effects. This chapter emphasizes the need for bacterial membrane vesicles modifications, provides an overview of characterization techniques, and outlines genetic engineering, click conjugation, lipid insertion, and membrane fusion strategies for producing engineered vesicles. Additionally, this chapter explores recent advances in bioengineered bacterial membrane vesicles for antimicrobial applications, including bacterial/viral vaccine development, anti-adhesion strategies, and potential in cancer therapy, gastrointestinal disease treatment, and osteoporotic bone defect repair.