The air passengers traffic forecasting has an enormous influence on the development of airport strategies and master plans with respect to both the airside and the landside. As the airport managers take their decisions based also on expected passenger volumes it is very important for them to be able to estimate the future demands as accurate as possible. This work deals with exactly this problem- how to develop a model to forecast air passenger demands based only on the historical passenger numbers data. The work will give a detailed description of the theoretical fundaments and the process of construction, calibration and validation for two methods that can be adopted by an airport- the Rational passenger numbers planning and the Box-Jenkins ARIMA methods. By making a forecast for the Vienna International Airport next to the theoretical description of the techniques also their correct use in practise will be shown and their accuracy will be proven.