This chapter discusses the pathology, durability and rehabilitation of concrete and also the conservation of renders in ancient buildings. The importance of cracks for the reduction of concrete durability is analyzed, followed by a description of the degradation mechanisms for this construction material. Measures to prevent the degradation of concrete are reviewed, including surface treatments and the use of electrochemical treatments to protect the steel reinforcement against corrosion. Regarding the renders in ancient buildings, particular attention is given to the crystallization of soluble salts. For these materials, the identification of its constituents and the requirements of conservation mortars are addressed.