According to previous measurements and models, classical DLVO surface forces sometimes cannot satisfactorily or even fail to interpret the experimental observations, which lead to the proposal of some non-DLVO surface forces such as hydrophobic force or hydration force. Meanwhile, the specific ion effects on bubble coalescence, which are governed by these DLVO and non-DLVO surface forces, are still obscure. Hence, the monograph intends to introduce several aspects for the fundamentals of surface forces at nanoscale, from approaches of classical thermodynamics and molecular simulations. This book, further refined at State Key Laboratory of Coal Mine Disaster Dynamics and Control in Chongqing University, has expanded our understanding towards the theoretical framework of extended-DLVO forces, for the support of applications related to aqueous film or air-liquid-solid interfacial interactions.