Quorum sensing (QS), which is modulated by cell density, is a signalling mechanism where bacteria coordinate collective behaviours by developing and recognizing tiny diffusible molecules known as autoinducers. QS is needed for environmental well-being, the continuation of life, and communication with host species such as plants, in both beneficial and harmful microorganisms. A detailed examination of QS processes is presented in this chapter, with a particular emphasis on Acinetobacter baumannii, an opportunistic pathogen whose multidrug resistance makes it more clinically relevant. One of the primary causes of multidrug resistance in bacteria is the formation of biofilms, one of the major factors that contribute to resistance. As QS promotes this biofilm formation, the overall amount of quorum quenchers has rapidly increased. The AbaI/AbaR mechanism is the main quorum sensing mechanism seen in Acinetobacter baumannii. AbaR is the receptor that regulates QS-responsive genes, and AbaI produces AHL molecules. Key characteristics like surface motility, biofilm formation, and antibiotic resistance are modulated by this system. To illustrate the conserved distinct regulatory factors, the QS mechanism in A. baumannii has been compared to that of other Gram-negative bacteria. To facilitate future investigations into this delicate signalling network, this chapter also outlines the methods for examining QS, including biosensor assays and analytical methods. Plant growth, defensive behaviours, and root structure are all regulated by QS molecules. In contrast, plants may modify microbial populations through the production of compounds that mimic AHL or by inhibiting bacterial signals. This mutual interaction regulates microbial colonization and simultaneously hinders pathogen emergence and supports beneficial plant-associated microbes. This chapter also points out an understanding of the genetic basis of QS, its ecological characteristics, and its therapeutic measures with insights into A. baumannii and its interactions with plant communities.