Overcrowding in Emergency Departments (ED) results in increased Lengths of Stay (LOS) and longer Waiting Times (WTs) for patients. These are ever-growing concerns in all hospitals around the world. Published literature shows many causes of this problem. This study, explores and identifies that one of the prominent causes can be attributed to human behaviour within EDs. It appears that patient behaviour has not been included in previous work as a cause of overcrowding. This thesis aims to present a method referred to as Discrete Event Simulation (DES) in an effort to explore and understand the effects of patient behaviour in the overcrowded ED of Tripoli Medical Centre (TMC). Firstly, a descriptive study was adopted, which collected data from different hospital sources, i.e. ED reports, ED's services time, staff and managers‘ opinions, and the observations of patients attending the ED of TMC. This identified the most significant behaviours impacting LOS and WT. Secondly, four different DES models were developed and analysed. Ultimately a hybrid model comprising of DES logic and Bayesian Network (BN) modelling was developed to capture and analyse a more accurate occurrence of human behaviour. Analysis of the hospital data reveals four behavioural factors are responsible for increasing WTs and LOS, leading to disruptions in patient flow. These factors include confrontation, challenges, passivity and illness belief. These behaviours are often appearing amongst the minor and non-urgent patients, who represent approximately 75% of all ED patients. The examination area within ED was found to be the place most commonly impacted by difficult behaviours, which is shown by the prolonged WTs in this area. A new strategy termed as Patient Behavioural Control (PBC) has been devised, developed and modelled. The PBC strategy aims to detect patient behavioural problems early and implements a revised patient flow procedure that results in overall reductions in LOS and WTs. This thesis contributes to the knowledge in this arena through consideration being directed towards patient behaviours from an operational perspective, utilising DES models in an effort to establish cause and effects, thus helping to devise a new approach in the healthcare sector. This new approach is not restricted in terms of application in only the healthcare arena, but can be adopted across other sectors for the management of human behaviours.