Probiotics are live microorganisms that provide health benefits to the host when ingested in adequate amounts. The most commonly used probiotic strains include lactic acid bacteria (LAB) and bifidobacteria. Probiotics have shown significant potential as therapeutic options for various diseases, but their mechanisms of action are not fully understood. Key mechanisms include modifying gut microbiota, competitive adherence to the mucosa and epithelium, strengthening the gut epithelial barrier, and modulating the immune system. Probiotics communicate with the host through pattern recognition receptors, such as toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-containing protein-like receptors (NLRs), which modulate signaling pathways like nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) to enhance or suppress activation and influence downstream pathways. These mechanisms are crucial for eliciting measured antimicrobial responses with minimal inflammatory tissue damage. Understanding these mechanisms will aid in selecting appropriate probiotic strains for specific applications and may uncover novel probiotic functions. The review explores the modes of action of probiotics, focusing on how gut microbes influence the host.Probiotics are live microorganisms that provide health benefits to the host when ingested in adequate amounts. The most commonly used probiotic strains include lactic acid bacteria (LAB) and bifidobacteria. Probiotics have shown significant potential as therapeutic options for various diseases, but their mechanisms of action are not fully understood. Key mechanisms include modifying gut microbiota, competitive adherence to the mucosa and epithelium, strengthening the gut epithelial barrier, and modulating the immune system. Probiotics communicate with the host through pattern recognition receptors, such as toll-like receptors (TLRs) and nucleotide-binding oligomerization domain-containing protein-like receptors (NLRs), which modulate signaling pathways like nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) to enhance or suppress activation and influence downstream pathways. These mechanisms are crucial for eliciting measured antimicrobial responses with minimal inflammatory tissue damage. Understanding these mechanisms will aid in selecting appropriate probiotic strains for specific applications and may uncover novel probiotic functions. The review explores the modes of action of probiotics, focusing on how gut microbes influence the host.