Marine plant polysaccharides (MPPs), which are purified from the major marine plants, namely, seaweeds (algae) and kelp, have gained significant attention owing to their multifunctional uses in biomedical and pharmaceutical applications through various routes. The major MPPs are alginate, carrageenans, agar, fucoidan, laminarin, and ulvan that have extensively used for oral delivery systems (ODSs) to impart needful functionalities in development of therapeutic dosage forms via their flexible unique features such as ease of tolerability, biodegradability, gelation ability, and responsiveness to environmental stimuli. Their structural heterogeneity allows them to exhibit antimicrobial, antioxidant, anti-inflammatory, and anticancer types of therapeutic activities. Such characteristics are widely explored in marine polysaccharides for conventional and novel DSs for various molecules via oral route. Furthermore, they find themselves to be key players in emerging platforms such as hydrogels, nanoparticles, microspheres, and implants that are enhancing controlled release of drugs, tissue healing, and target disease specificity. Hopeful opportunities notwithstanding, complications remain to check standardization, structural variety, stability, and approval by regulating bodies. Further research and development of extraction methods, functional amendment, and sea biology are indispensable in maximizing their potential for drug delivery. This chapter comprehensively addresses about the effective scenario of marine plant-derived polysaccharides for various flexible functionalities in oral delivery of various molecules as per rationale of the required dosage form preparations.