This document discusses the clinical significance and principles of tooth preparation for operative dentistry. It covers 3 main areas: biological considerations to minimize damage to adjacent teeth and soft tissues, mechanical considerations to maximize retention and resistance of restorations, and esthetic considerations for margin placement and tooth contours. Biological factors include using matrices, tapered diamonds, and aspirators to protect adjacent teeth and soft tissues. Mechanical factors focus on preparation taper, surface area, stress relief, and luting agents to enhance retention and resistance to dislodging forces. Margin placement aims to be supragingival when possible for hygiene and visibility.