Diary methods allow researchers to examine processes in daily life in a way that is not possible using traditional methods. Using diaries, researchers can obtain repeated observations on psychological variables over hours, days, and weeks. Diary data, however, present several data analytic challenges stemming from the various possible sources of interdependence in these data. The multilevel or hierarchical linear model (HLM) provides a flexible set of analytic tools that can take account of these complexities.