The problem addressed in this D.Phil. thesis is the aggregation of welfare data across individuals and over time, in particular to construct measures of poverty which reflect an ethical poverty analyst.'s normative judgements regarding trajectories of wellbeing experienced by individuals in a society. The motivation' for the analysis is the provision of tools useful for the evaluation of poverty alleviation policies. Specification of appropriate assumptions concerning the information available to the poverty analyst and weak restrictions to her method of evaluation create a frame- work in which the consequences of normative judgements may be elucidat.ed. In this process some well known results in micro economic theory are generalised, rendering them applicable to the domain of analysis. Weak consistency properties together with anonymity are shown to restrict the class of available poverty measures to those which induce a well-defined ordering of the space of wellbeing trajectories. Particular properties of the trajectory ordering are motivated and imposed to de- velop a new class of int.ertemporal poverty measures which permit less intertemporal compensation of wellbeing as depth of poverty increases. It is shown that. this property precludes pure duration-sensitivity, making the intertemporal poverty measures pro- posed inapplicable to the measurement of chronic poverty. It is shown also that there exists a conflict between reasonable assumptions about intertemporal preferences and the measurement of chronicity or persistence of poverty, with the consequence that many recently suggested 'chronic poverty measures' are in fact insensitive to chronicity of poverty. A different measure is proposed, with properties which render it applicable to the measurement of chronic poverty. Imposing equivalence of the two measures for constant-wellbeing trajectories permits decomposition into chronic and transient com- ponents. These measures are applied to the analysis of poverty in rural Ethiopia in the period 1994-2004.