The Netherlands Twin Register (NTR) consists of individuals who have agreed to participate in twin-family studies and was established and is managed by the Department of Biological Psychology, VU University Amsterdam (see: https://tweelingenregister.vu.nl/). The NTR was established in 1987 and has enrolled around 120.000 twins and a roughly equal number of their relatives. The majority of twin families have participated one or more times in survey studies on a host of epidemiological variables including social demography, personality, lifestyle, somatic and mental health, and subsamples took part in biomaterial collection (e.g. DNA) and dedicated projects for e.g. neuropsychological, biomarker, and behavioural traits. The recruitment into the NTR is fully inclusive without any restrictions on enrolment. The NTR is committed to actively seek the commitment of its participants to science and their continued involvement in NTR research by maintaining a website, electronic newsletters, and the MijnNTR portal that provides personalized feedback to participants. The NTR resources, e.g. the longitudinal phenotyping, the extended pedigree structures, and the multi-generation genotyping allow for future twin-family research that will contribute to gene discovery, causality modelling, and studies of genetic and cultural inheritance of behavioural traits and mental and physical health. In the CD2 portal, only the NTR projects for children and adolescents (<18 years of age) have been included. This is refered to as the Young Netherlands Twin Register (YNTR).