According to modern physics, many objectively improbable events actually occur, such as the spontaneous disintegration of radioactive atoms. Because of high levels of improbability, scientists are often at a loss to explain such phenomena. In this main essay of this book, Wesley Salmon offers a solution to scientific explanation based on the concept of statistical relevance (the S-R model). In this vein, the other two essays herein discuss "Statistical Relevance vs. Statistical Inference," and "Explanation and Information."