The Genetics of Sexuality and Aggression (GSA) project was launched at the Abo Akademi University in Turku, Finland in 2005 and has so far undertaken two major population-based data collections involving twins and siblings of twins. To date, it consists of about 14,000 individuals (including 1,147 informative monozygotic twin pairs, 1,042 informative same-sex dizygotic twin pairs, 741 informative opposite-sex dizygotic twin pairs). Participants have been recruited through the Central Population Registry of Finland and were 18-49 years of age at the time of the data collections. Saliva samples for DNA genotyping (n = 4,278) and testosterone analyses (n = 1,168) were collected in 2006. The primary focus of the data collections has been on sexuality (both sexual functioning and sexual behavior) and aggressive behavior. This paper provides an overview of the data collections as well as an outline of the phenotypes and biological data assembled within the project. A detailed overview of publications can be found at the project's Web site: http://www.cebg.fi/.Keywords: aggression, environmental, genetic, population based, sexuality, twin studyThe Genetics of Sexuality and Aggression (GSA) project in Finland has completed two major data collections since its inception in 2005. The major research goals of the GSA project are to conduct investigations with genetically sensitive designs, in large, population-based samples, on phenotypes related to sexuality and aggression. What makes this data bank unique is its focus on sexuality and aggression-related phenotypes that have rarely been studied in population-based samples. For several of these phenotypes, the GSA samples are the largest genetically informative samples in the world. Most of our research has focused on sexuality and gender identity-related phenotypes, such as sexual function and dysfunction, sexual behavior and its variations, and body image. A number of relevant psychiatric phenotypes have also been measured (e.g., behaviors and attitudes related to eating, and psychopathology such as anxiety and depression). Furthermore, the research site has a long history of conducting aggression research with genetically informative designs (in both mice and humans), which is now continued within the framework of the GSA project. For example, a major research goal of the GSA project is to examine genetic effects on aggressive behavior, including identifying genes that moderate the association between alcohol use and aggressive behavior.The project is conducted at the Department of Psychology and Logopedics at the Abo Akademi University in Turku, Finland. From the second data collection (carried out in 2006) onwards, collaborations with the Department of Pharmacology at the Sahlgrenska Academy, University of Gothenburg, Sweden, have been undertaken in order to collect biological markers. For a subset of the second data collection, genotype data is available, as well as data on free testosterone (T) levels, both collected by means of non-invasive saliva sampling. For the ...