The reports in this section demonstrate several ways in which longitudinal research with twins is informative for the study of development. All of these twins have been followed for long time periods. These results are the latest stage of study for each. By virtue of their long-term nature, together these studies provide information on patterns and changes in several developmental areas from infancy to adulthood. They also document when specific variables no longer exert any influence on development. The first report, by Alin Akerman and Suurvee (“The Cognitive and Identity Development of Twins at 16 Years of Age: A Follow-up Study of 32 Twin Pairs”) is a study of twins followed from birth to 16 years of age. The second report, by Ebeling, Porkka, Penninkilampi-Kerola, Berg, Jarvi, and Moilanen (“Inter-twin Relationships and Mental Health”), is a study of twins followed from pregnancy to 22–30 years of age. The third report, by Lange (“Coping Ability at Midlife in Relation to Genetic and Environmental Influences at Adolescence”), is a study of twins and singletons followed from 10 to 16 years of age to 35 years of age. The section attests to the perseverance of these authors as researchers, and to the strength of the personal relationships of these authors with the individuals in their projects.