This paper introduces 4GM, a semi-structural model for monetary policy analysis and macroeconomic forecasting in Colombia.This model is based on a New-Keynesian rational expectation framework for an oil-exporting small open economy.In this paper, we present the model structure and examine the response of its variables to domestic, foreign and oil-price shocks.Further, we assess 4GM in terms of its historical shock decomposition and its out-of-sample forecasting.