This note defines what econometrics is. The differences between models and economic models are brought out. The six steps involved in econometric model building are (a) statement of theory of hypothesis, (b) specification of theoretical econometric model for testing theory, (c) estimation of the parameters of the model, (d) evaluation of estimates of parameters of the model, (e) evaluation of the forecasting performance of the model, and (f) further use of empirical econometric model. Data constraints in building model are discussed.