This book is a compilation of the current developments from the interface science and technology research results of the authors and their co-workers for a long term. It is a systematic presentation of basic knowledges about interface science concerned with mechanical engineering. There are fifteen chapters in the book, including analysis of the solid surface structure, properties of solid surfaces, properties of liquid and its surface, solid-liquid interface, gas-solid interface, solid- solid interface, ordered molecular films, surface micro-wear, interface problems in computer hard drive, microscopic flow of the solid-liquid interface, surface modification and coating, interface micro-tribology, experimental analysis of surface and interface, surface electric effects and its applications, adhesive applications. The book can be served as a valuable reference for graduate-level students, teachers and practicing engineers majoring in mechanical engineering or the related fields.