This article discusses physical modelling and model-based sound synthesis techniques related to the development of computational simulations of plucked string instruments. It demonstrates how the more "physical" waveguide model of a plucked string can be reduced to an extended form of the Karplus-Strong type termed the single delay-loop (SDL) model. This article contains information on the Karplus-Strong (KS) algorithm, fundamentals of string behaviour, details on bi-directional digital waveguides and the single delay-loop (SDL) model and elaborates on the techniques for modelling a plucked string with bridge output.