Before diagnosing the causes of deterioration or failure of a concrete structure, a sound understanding of the physical, chemical and mechanical actions that lead to defects is necessary. Methods for studies of the structural condition and residual carrying capacity should be composed separate for each structure, taking into account the properties of the materials, calculation methods, designed exploitation purposes applicable in the period of building, extent of damage and a possible effect on the carrying capacity of the structure. Generally, only after the cause or causes are known can rational decisions be made concerning the selection of a proper method of repair and in determining how to avoid a repetition of the circumstances that led to the problem. This book focuses on the causes of inadequate duration of old damaged reinforced concrete structures. Also, an estimation and analysis of residual carrying capacity is presented. As a result of the studies, possible restoration solutions are provided.