Casting technology, possessing a deeply rooted history in the shaping of engineering materials, is a superior manufacturing method that enables the production of complex geometries as a single monolithic piece with high strength values. However, in industrial practice, the disconnect between design and production processes and the lack of awareness among designers regarding metallurgical processes often lead to manufacturability issues, cost increases, and quality losses. This book chapter systematically addresses the principles of “Design for Casting” for design engineers and manufacturers, in the light of theoretical infrastructure and practical applications. The study primarily examines the decisive role of fundamental physical phenomena-such as liquid metal fluidity, solidification shrinkage, heat transfer, and directional solidification-on part geometry. Particular emphasis is placed on aligning idealized models created in Computer-Aided Design environments with the thermodynamic realities of the foundry floor. In this context, critical construction rules such as uniform wall thickness, the wedge rule in section transitions, management of hot spots at junction points, rib design, core strength, draft angles, and the optimization of machining allowances are detailed through right-wrong comparisons. Furthermore, the role of casting simulation technologies in the design process and the perspective of sustainable production are discussed. Consequently, this study aims to guide the designer to foresee not only the functional requirements but also the solidification journey of the metal within the mould, thereby enabling the design of defect-free, economical, and high-quality casting parts.