Abstract: It has been known that the most satisfactory method of determining rate constants and activation parameters is a full steady-state line-shape fitting orer the temperature range where exchange effects can be observed. For weakly coupled systems undergoing exchange it is possible to compute theoretical ine shapes using modified Bloch equation, but strongly coupled systems require a full density matrix (DM) treatment. The aim of this paper is to show how-to calculate line-shapes using the DM method. The paper consists of the basic theory of DM and the applications of DM theory to NMR line-shape calculations of inter-and intra-molecular exchanging systems.