Engineering structures are made of materials from matter found in the universe. At every level-atomic, nano, micro, and macro-the components in the matter interact with each other and merge together continuously, assuming various states that, for example, identify initiation (birth) to the end or failure (death). The interaction or coupling plays a significant role in the response of materials and hence, engineering systems. Then, the coupling under external influences or forces at the micro level between particles, fluid, air, temperature, and chemicals in a material element, between structural and geologic materials at interfaces, and between rock masses and joints is of utmost importance. Thus, the understanding and the characterization of the behavior of materials are vital for the solution of geotechnical systems. This book attempts to address these issues.