Single-crystal materials machining involves complex interactions between the cutting tool and the material, significantly influenced by the material’s unique anisotropic properties and the transition between brittle and ductile cutting modes. Single-point diamond turning (SPDT) is a crucial machining method used for shaping single-crystal materials to achieve desired surface morphologies. However form accuracy and performance are substantially affected by the machined surface of single-crystal materials' presence of a ductile–brittle alternating pattern (DBAP). This chapter provides a comprehensive overview of these cutting mechanisms, focusing on the critical phenomena of brittle-ductile transition (BDT) and the insights gained from molecular dynamics (MD) simulations.