  In this survey we discuss the recent causal panel data literature. This
recent literature has focused on credibly estimating causal effects of binary
interventions in settings with longitudinal data, emphasizing practical advice
for empirical researchers. It pays particular attention to heterogeneity in the
causal effects, often in situations where few units are treated and with
particular structures on the assignment pattern. The literature has extended
earlier work on difference-in-differences or two-way-fixed-effect estimators.
It has more generally incorporated factor models or interactive fixed effects.
It has also developed novel methods using synthetic control approaches.
