Waxes are a group of organic solid or semi-solid materials with relatively high molecular weight (typically ranging from 400 to 10,000 g/mol), which are widely used in polymer, coating, adhesive, rubber, pharmaceutical, and packaging industries. Waxes have become key additives in the design and engineering of polymer systems owing to unique properties such as a distinct melting point, significant crystallinity, hydrophobicity, chemical stability, and structural modifiability. In this review, the role of waxes in polymer science is defined, followed by a classification based on their chemical structure (hydrocarbon and functionalized types). Subsequently, waxes are classified based on their chemical structure into two main categories: hydrocarbon waxes (including polyolefin waxes and Fischer-Tropsch waxes) and polar waxes (including amide waxes, oxidized polyethylene waxes, ester waxes, and copolymer waxes). Various production methods of polyolefin waxes (including high-pressure radical polymerization, Ziegler–Natta and metallocene catalysis, thermal degradation, and production from recycled materials) are analyzed in detail. Moreover, Fischer–Tropsch, amide, ester, oxidized, and copolymer waxes are examined in terms of structure, properties, and synthesis process. Finally, the engineering applications of waxes across nine major industrial fields are presented. By analyzing the structure–property–application relationships, this review outlines future research directions for the development of engineered and bio-based waxes.