Alginate, a polymer mainly derived from seaweed, has garnered significant attention owing to its renewability, biocompatibility, biodegradability, and exceptional gel formation characteristics, rendering it highly versatile for numerous applications. Recognizing the imperative for tailored bulk materials, this review scrutinizes the processing methodologies of alginate-based bulk materials and delineates strategies to improve their properties, encompassing ionic crosslinking, plasticization, and hybridization with other polymers and/or fillers. It explores noteworthy alginate-based blends with natural polymers like polysaccharides and proteins, alongside fossil-based polymers like poly(vinyl alcohol). It also examines alginate-based composites incorporating various nanofillers such as cellulose nanoparticles, graphene, and nanoclays. The processing techniques for these multiphase alginate-based systems encompass solution casting, coating, spinning, 3D printing, and thermomechanical processing. Strategies for crosslinking alginate, plasticizing it, and optimizing its interactions with other polymers/fillers are outlined, bearing repercussions on the resultant materials properties. This review emphasizes the structure–process–property relationships of these multiphase systems in bulk and highlights synergistic effects and potential impediments to property improvements. It surveys prospective applications for alginate-based multiphasic bulk materials, spanning membrane separation, controlled release, wound healing, tissue engineering, food packaging, and agricultural domains. Finally in this field, knowledge gaps have been identified and future research directions are suggested.