Why does a coat of whitewash on a wall surface often shed or peel off? A vast majority of the metallic surfaces of primary electronic components are coated with a man-made, or naturally occurring, protective coatings layer. Such layers also frequently peel off. Why is that so? Because almost all primary components of electronic devices are made of thin films, the shedding or peeling off of such thin films is one of the important reasons why these devices fail. Why do such thin films peel off? Thin films come in many different types and varieties. When they go "bad," what common and regular characteristics do they share? This chapter begins with an overview of thin films, and then proceeds to discuss their mechanical properties in terms of stress-strain analysis, residual stress, and their fracture toughness; as well as the polarization of ferroelectric thin films and the bending of ductile thin films.