The immune system is the primary defense mechanism that protects the body from infections, as well as it contributes to the overall well-being of organisms. Seaweeds are found to contain many bioactive compounds, such as polysaccharides, phlorotannins, fucoidans, and sulfated galactans, with immune-modulatory activity. These compounds appear to potentially enhance both innate and adaptive immune responses such as pseudopodia formation, cytokine production, and modulation of immune signaling pathways. Studying the bioactive components from seaweeds for immunomodulatory activity opens a new avenue toward the development of natural therapeutic agents, which could immunostimulate efficacy for managing immune dysfunction. The chapter aims to understand the possible mechanisms through which these effects take place and emphasize the potential of seaweed-based products for immune health.