ABSTRACT
This chapter deals with models and modelling, starting with an exposition of the ubiquitous role of models in all research and attempting a broad classification of models backed up with illustrations. Different types of models are used in different contexts and the chapter devotes a section to each of the following topics: probability models, stochastic process models, growth models, regression models, structural relations models, optimization models and models to validate different types of analysis to be carried out on the data collected. Some special types of models with lesser extent of applicability have also been considered. The way new models are being worked out and the need for developing such new models have been hinted at as open problems for research.
