Additive manufacturing (AM), commonly known as 3D printing, has transformed modern materials engineering by enabling complex geometries, reduced material waste, and rapid prototyping. Despite these advantages, the quality of AM-produced materials remains a critical challenge, influenced by microstructural heterogeneity, porosity, residual stresses, and anisotropic mechanical behavior. This paper provides a comprehensive review of the factors affecting the quality of metallic, polymeric, and composite 3D printed materials. Key microstructural characteristics, process parameters, post-processing techniques, and quality assessment methodologies are analyzed. Strategies for optimizing material performance through parameter control, heat treatment, and surface finishing are discussed. Emerging approaches such as in-situ monitoring, machine learning-based process optimization, and multi-material printing are evaluated. The study concludes with perspectives on future research directions to achieve high-quality, reliable AM components suitable for aerospace, biomedical, and industrial applications [1].