Each queueing phenomenon where clients demonstrate some heterogeneity in terms of arriving to the system (intensity, way of arriving, ....), service times (mean service times, variability, ...) and/or Quality-of-Service expectations (short anticipated delays such that some service priority is needed for some customers, ...) can be regarded as a multi-class queueing system. These systems require more intricate models than single-class systems, and the complexity of mathematical analysis, which is necessary to be able to predict the performance of the system, also increases.. The aim of this project is the modeling and analysis of several queueing phenomena as multi-classes queueing models. Application areas are a.o. (wireless) communication systems, quantum networks, transport networks and waiting lists in healthcare.