Methodology: Models, reality, properties of models, system characterisation, steps in building mathematical models, source or errors, dimensional analysis, model classification and illustration. Basic themes: counting, estimation and structuring, types of structural equations and analysis with examples, graphical models, simulation models and Monte-Carlo method, parametric analysis. Case Studies: Biology and medicine, communications and information technology, mechanical vibrations, hydrodynamics, chemical systems, thermodynamical systems, social, economical and behavioural applications, ecological systems, transport systems, image processing, space technology, agricultural sciences etc.