This book covers the corrosion of mild steel in weak acid aqueous solutions, such as those containing organic acids, dissolved carbon dioxide and/or hydrogen sulfide. The largest application of this is in corrosion/integrity of pipelines and facilities in production and transportation of oil and gas, but also in sequestration, transportation and injection of carbon dioxide related to reduced emissions and climate change. The book starts out with presenting the theoretical basis of corrosion in terms of electrochemical thermodynamics and electrochemical kinetics. It then focuses on corrosion mechanisms of mild steel in aqueous organic acid solutions, followed by corrosion in aqueous carbon dioxide solutions, and finally aqueous hydrogen sulfide solutions. Finally, modeling of mild corrosion in those environments is described.