The main objective of the MISTELA model is to integrate the different aspects of strategic planning of TELEFONICA DE ESPAÑA into one signal unit. By so doing one is obviously forced to give up many of the small details in order to be able to look at the larger picture. MISTELA uses a systemic approach to construct the model described in, this paper, Systems Dynamics was chosen, since this technique permits straightforward combination of different modelling procedures such as statistical inference, calibration by trail and error, linear and/or quadratic programming, etc. To give an idea of the size of the model, it handles about 1,500 equations, definition and identities. There are some 700 conceptual variables, and because many of these are vectors, in effect there about 4,000 scalar variables.