Abstract: Challenges due to erosion-corrosion in oil and gas production are briefly reviewed. The achievements of the author's group on the modeling of synergistic effects erosion are summarized. The erosion-corrosion mechanisms, the methods to evaluate the erosion-corrosion resistance of materials and the approaches to mitigate the damage caused by erosion-corrosion are discussed in this article. This article is presented in two parts. Part 1 focuses on the background, the concepts relating to synergism of erosion/corrosion and corrosion in erosive fluids.