In contemporary labour economics increasing attention is paid to the fact that unemployment is not only a stock but also a flow phenomenon. The present micro-econometric study analyses the impact of important socio-economic characteristics on unemployment duration in West Germany. Based on a search theoretic framework unemployment duration is considered as a stochastic process whose evolution is influenced by economic and demographic variables like unemployment benefits, expected wage offers, training and age. This is modelled by application of the concept of the hazard rate which denotes the conditional exit rate from unemployment over time given elapsed unemployment duration. Contrasting more traditional models a semi-parametric approach is chosen which reduces the danger of mis-specification of the stochastic duration process. This procedure also is particularly suitable for the analysis of grouped observations on unemployment duration typically generated by longitudinal data sets as the German "Socio-Economic Panel" which is utilized for this study. Besides deriving a set of empirical results on unemployment duration in West Germany methodological issues of duration analysis are considered with particular attention paid to the impact of the sample design. Also, important outcomes from search theory and findings from other hazard rate analysis are surveyed.