The focus of this book is on the management of dynamic inbound contact centers with impatient customers and retrials. we consider contact centers with both homogeneous and heterogeneous customers and agents. The term dynamic refers to the processes in a contact center in two ways. Firstly, these processes are random and secondly they depend on the time of the day and the day of the week. The processes are the successive arrivals of customers to the contact center, the consecutive services by agents, and the successive abandonments and retrials of customers. In order to consider both aspects we use the so-called strong approximations. By means of this approximation performance measures are derived and analysed of different contact centers. Thereby an essential poimt of this book is the influence of retrials and impatient customers on the performance, the staff requirement planning and the shift scheduling decisions in big contact centers.