Abstract: The first part of this thesis deals with the incorporation of restrictions on working hours in microeconometric models of labour supply. In this thesis, the restrictions on working hours are identified on the basis of subjective labour supply data. As the use of subjective data is not (yet) common in economics, chapter two tests the predictive value. Using the subjective labour supply data, chapters three and four model and estimate the restrictions on working hours. The second part of this thesis deals with the common opinion that within the German apprenticeship system large firms invest in the general skills of their apprentices. Chapter five studies the consequences of two competing theories explaining this behaviour, and analyses mobility and wages of graduated apprentices in their first job to distinguish empirically between the two theories.