This chapter offers an overview of etching, a vital process in semiconductor chip manufacturing for removing unwanted material. It delves into etching mechanisms, including wet etching (chemical reactions) and dry etching (plasma), covering techniques like reactive-ion etching (RIE), deep reactive-ion etching (DRIE), and sputter etching for wet etching, and isotropic and anisotropic etching for dry etching. Performance metrics such as etching rate, selectivity, profile control/surface quality, and environmental/safety considerations are examined. Furthermore, the chapter explores diverse applications of etching, spanning semiconductor chip manufacturing, printed circuit board designs, MEMS, and semiconductor advanced packaging.