Arsenic is viewed as being synonymous with toxicity, and now arsenic in natural waters is a worldwide problem. Among twenty-one countries' people are affected by groundwater arsenic contamination, like the Bangladesh, India and China. In this book, readers can get an overview of arsenic background information and available arsenic remediation methods. In this work, a model for predicting arsenic adsorption on iron coated sand based on surface complexation modeling was developed. The model can be used to calculate the arsenic adsorption performance with variable initial arsenic concentration and over the pH range 5 to 8 when the following data are available: 1) maximum adsorption capacity of the adsorbent, 2) initial arsenic concentration and mass of the adsorbent, and 3) pH value. The average difference between model calculation results (shown in this work) and experimental results from three experimental studies is less than 5%. Additionally, based on the improved model correlation provided by the bidentate assumption, there is a strong case for the main surface complexes between arsenic and Fe-sand being bidentate complexes.