Panel data, also known as longitudinal data, is a type of data that contains observations about different cross-sections across time. Panel data is a subset of longitudinal data where observations are for the same subjects each time. Examples of groups that may make up panel data series include countries, firms, individuals, or demographic groups. Panel data can model both the common and individual behaviors of groups, contains more information, more variability, and more efficiency than pure time series data or cross-sectional data, and can detect and measure statistical effects that pure time series or cross-sectional data cant. Panel data can minimize estimation biases that may arise from aggregating groups into a single time series. Panel data examples can be found in economics, social sciences, medicine and epidemiology, finance, and the physical sciences.

In panel data, variables should be in columns, and entity and time in rows. This format is known as long form. Panel data analysis is widely used in economics to study the behavior of various micro and macroeconomic variables.