This chapter presents an overview of the significance of surface micro-topography (SMT) in ultrasonic-assisted machining (UAM) processes. It explains the fundamental principles of ultrasonic vibrations, specifically linear, elliptical, and three-dimensional modes, and how they are effectively applied in various machining techniques such as turning, drilling, and milling. Key parameters related to SMT, such as contact angle, wettability, and anisotropic wettability, are discussed in the context of characterizing and evaluating surface quality and behavior. The wide range of SMT applications in both industrial manufacturing and medical fields is also discussed, with an emphasis on how surface textures influence functional performance.