The present book gathers a large amount of the recent research results on this topic to provide a better understanding of the size effect by giving a quantitative description of the relationship between the properties of engineering concrete-making material (e.g. the nominal strength) and the corresponding structure size. To be precise, this is about to explore the new static and dynamic unified size effect laws for concrete materials, as well as size effect laws for concrete components. Besides presenting clear and accurate descriptions that further deepen our fundamental knowledge, this book provides additionally useful tools for the scientific design of concrete structures in practical engineering applications.