Microalgae hold great promise as sustainable feedstocks for a broad spectrum of biotechnological applications. However, their use is still constrained by the significant financial and energy demands of downstream processing, particularly biomass harvesting and extraction of high-value metabolites. A major barrier represents their robust, often biochemically complex cell wall that hinders efficient processing. Because cell-wall biosynthesis consumes large amounts of photosynthetically fixed carbon, the wall itself represents not only a major metabolic investment but also a largely untapped, renewable bioresource with significant industrial potential. To advance algal biotechnology, comprehensive knowledge of cell-wall structure, biosynthesis, and variability is essential. However, for Chlorophyta—the green algae most frequently used in biotechnological applications—available information on cell-wall composition remains fragmented. Existing studies often describe divergent or even contradictory findings, reflecting the remarkable diversity of cell-wall architectures within this phylum. This review addresses this knowledge gap by synthesizing and critically evaluating current research on Chlorophyta cell walls. An outline of the major structural components reported across species, including polysaccharides, glycoproteins and algaenan-like materials is provided. In addition, current industrial applications of these cell-wall components—ranging from biomaterials and bioactive compounds to environmentally friendly polymers—are discussed, along with their potential roles in future biotechnological innovations. By integrating these scattered data, the review aims to provide a unified perspective that supports both fundamental research and practical application. Ultimately, this review seeks to facilitate the development of more efficient biotechnological processes and to advance a more sustainable bioeconomy by strengthening the understanding of the biochemistry of Chlorophyta cell walls.