Data captured at different points in time provides the basis for longitudinal research. It is unquestioned that several IS phenomena deal with change over time such as post-adoption behavior with respect to IT artifacts. However, cross-sectional research designs are predominantly applied in the IS field up till now. This paper is therefore written not only to motivate the IS community to apply longitudinal research to time-variant IS phenomena but also to discuss common pitfalls. For this purpose, we outline various longitudinal studies and provide four guidelines that should be considered during their planning. In particular, common methodological issues like space and amount of repeated observations or attrition are discussed. Finally, an overview of common longitudinal research questions and corresponding methods of longitudinal analyses is provided.