The goal of this project is to analyse human resource developments and their determinants using administrative, internal personnel data of two firms, one active in the service and the other active in the manufacturing sector. For the first time “insider econometrics” can be applied at ZEW because detailed personnel panel data of all employees containing all relevant information (qualification, career, training, tenure, wages) are available. With the data of the service sector firm we will analyze two different topics, first the participation of older workers in further training and second the participation decisions of young mothers after maternity leave. For the second firm we will investigate the effects of demographic changes on the structure of their workforce.