Proteins, in particular, must be able to interact with other polymers, for enzymes are involved in the synthesis and degradation of all biopolymers. In addition, however, many examples are known of associations between nonenzymic proteins and other proteins, polysaccharides, or nucleic acids. Muscle movement, for example, is brought about and controlled by complex interactions between several proteins (myosin, actin, troponin, and tropomyosin) while collagen fibers are associated with both glycoproteins and proteoglycans in connective tissues. Protein antibodies can bind to protein or polysaccharide antigens, while polypeptide hormones must be recognized by their receptors, themselves proteins or glycoproteins. The proteins that interact with nucleic acids (e.g., repressors) bind to specific base sequences or secondary structures on the polymeric acids. In some cases these base sequences are almost palindromic (read the same backward or forward) as in XV, and the protein molecules which bind to them often have two subunits so that one may bind to each strand of the DNA. A “motif” found in several DNA-binding proteins consists of two helices linked by a short stretch of polypeptide chain in the form of a sharp bend. Such an arrangement fits easily into a groove of double helical DNA. Within ribosomes, strong interactions between protein and r-RNA are essential for maintenance of the structure and functioning of the ribosome. Details of these interactions are not yet well understood. Polysaccharide-polysaccharide interactions can also take place, probably involving extensive hydrogen bonding and “shape fitting” over lengths of twenty or more monosaccharide residues. This is important in plant cell walls where cellulose fibers are embedded in a matrix of proteins and several different polysaccharides. Utilization of biopolymers for 3D printing technologies and their promising use in different fields of aerospace, textile, food, biomedical, and bioindustrial applications are of substantial academic, environmental, and social interest. This chapter reviews the state-of-the-art additive manufacturing (AM) of biopolymers, with a particular focus on cellulose, lignin, alginate, chitosan, starch, polylactic acid (PLA), and polycaprolactone (PCL). AM comprises a subset of processes that converts a computer-aided design (CAD) into a metallic, polymeric, ceramic, or composite structure in a layer-by-layer manner. 3D printing offers substantial advantages over other currently employed polymer fabrication methods, for instance, cost effectiveness, rapid fabrication of intricate designs, quick modification of models, reduced production cycle time, as well as manufacturing of multimaterial objects. Different approaches have been developed, such as continuous extrusion, droplet delivery (typically, 3D inkjet printing), selective laser sintering, electron beam melting, and the use of ultraviolet (UV) light to cure selected areas in photosensitive polymer resins (for instance, stereolithography or two-photon polymerization). The deployment of a specific approach for making 3D objects depends excessively on a material's specification. For example, materials like starch can be printed through an extruder, while some nonprintable food by nature, such as meat, vegetables, and rice, must be processed in powder/paste form before being subjecting to 3D printing. Based on the intended application, the requirement of material properties also varies significantly, as illustrated For example, the biomedical field requires a material to exhibit a holistic characteristic in terms of printability, biocompatibility, degradability, and mechanical properties. On the other hand, textile products require adequate flexibility, resilience, and tensile strength in compliance with the wearer's comfort and body movement. Furthermore, 3D printed food products should be edible, easily printable, and display resistance toward shape deformation during postprocessing (e.g., baking, cooking, and frying). Additionally, with the rapid increase in consumption of 3D printing materials, plastic pollution (both landfill and marine) is growing significantly. The use of bioplastics that are also biodegradable, instead of petroleum-derived plastics, can reduce 3D printing waste, save thousands of marine species every year, and reduce severe landfill pollution. However, the mechanical properties of 3D printed biopolymers are not often comparable to their petroleum-derived counterparts, which restricts the use of biopolymers in the applications that demand structural rigidity. Therefore lots of research work is currently in progress to address the issue related to the mechanical properties of 3D printed biopolymers.