Only with panel data is it possible to control for unobserved heterogeneity.  Panel surveys are, however, more costly and complex than cross-sectional studies and this imposes several challenges in terms of planning and design. Issues related to planning and management include reconciling long-term needs and short-term resources, ensuring the comparability of measures from wave to wave, combining longitudinal analysis with cross-sectional analysis, documenting survey activities, and disseminating the outputs in a timely fashion. These issues are all discussed in this paper which makes some specific recommendations based on a review of the international experience.