Econometrics has become an integral part of training in modern economics and business. Together with microeconomics and macroeconomics, econometrics has been taught as one of the three core courses in most undergraduate and graduate economic programs in the world. This chapter discusses the philosophy and methodology of econometrics in economic research, the roles and limitations of econometrics, and the differences between econometrics and mathematical economics as well as mathematical statistics. A variety of illustrative econometric examples are given, which cover various fields of economics and finance.