A high-complexity blend of β-glucans from Saccharomyces cerevisiae induces potent trained immunity in human primary monocytes, leading to enhanced innate immune responses. This study shows that the β-glucan preparation ABB i16, derived from S. cerevisiae, is more effective than β-glucans from Candida albicans or other yeast β-glucans in inducing trained immunity. The induction requires Dectin-1, CR3, TLR4, and other receptors, as well as downstream signaling molecules like Raf-1, Syk, and PI3K. The β-glucan components synergistically activate multiple pathways, resulting in a robust secondary immune response upon unrelated challenges. In vivo murine models of melanoma and bladder cell carcinoma show that pre-treatment with ABB i16 β-glucan significantly reduces tumor growth. The study highlights the potential of β-glucan-based therapies for cancer and infectious diseases by enhancing innate immune memory and protective responses. The findings suggest that ABB i16 β-glucan could be a valuable tool for developing novel immunotherapies. The research also identifies the key receptors and signaling pathways involved in β-glucan-induced trained immunity, providing insights into the molecular mechanisms underlying this phenomenon. The study underscores the importance of understanding the immunological mechanisms of yeast-derived β-glucans to harness their immunostimulatory potential effectively.A high-complexity blend of β-glucans from Saccharomyces cerevisiae induces potent trained immunity in human primary monocytes, leading to enhanced innate immune responses. This study shows that the β-glucan preparation ABB i16, derived from S. cerevisiae, is more effective than β-glucans from Candida albicans or other yeast β-glucans in inducing trained immunity. The induction requires Dectin-1, CR3, TLR4, and other receptors, as well as downstream signaling molecules like Raf-1, Syk, and PI3K. The β-glucan components synergistically activate multiple pathways, resulting in a robust secondary immune response upon unrelated challenges. In vivo murine models of melanoma and bladder cell carcinoma show that pre-treatment with ABB i16 β-glucan significantly reduces tumor growth. The study highlights the potential of β-glucan-based therapies for cancer and infectious diseases by enhancing innate immune memory and protective responses. The findings suggest that ABB i16 β-glucan could be a valuable tool for developing novel immunotherapies. The research also identifies the key receptors and signaling pathways involved in β-glucan-induced trained immunity, providing insights into the molecular mechanisms underlying this phenomenon. The study underscores the importance of understanding the immunological mechanisms of yeast-derived β-glucans to harness their immunostimulatory potential effectively.