Longitudinal indicators are measures of an individual or family behavior, interaction, attitude, or value that are assessed consistently or comparably across multiple points in time and cumulated over time. Examples include the percentage of time a family lived in poverty or the proportion of childhood a person lived in a single-parent family. Longitudinal indicators reflect exposure not at a "snapshot" moment but over the lifecourse and may also be more reliable assessments of the family environment or experience. We highlight potential longitudinal indicators and discuss methodological issues.