Wider research context: Children of LGBTQ parent families are part of a family, in which at least one parent identifies as lesbian, gay, bisexual, transgender, queer, or with another non-heterosexual sexual orientation or non-cisgender gender identity. Recent sociolegal developments led to an increasing number of these families in Austria, but there is a dearth of local research on children’s psychological adjustment and family functioning. This is compounded by a general lack of theory as well as limitations to traditional statistical methods used in this field. These empirical, theoretical, and statistical gaps impede effective policy making to safeguard children’s mental health and to protect them from discrimination. Objectives: In the Rainbow Austrian Longitudinal Family (RALF) Study, we aim to advance the field by empirically testing our proposed Risk and Resilience Model of LGBTQ Parent Families within the first longitudinal research cohort of these families in Austria. We will comprehensively assess risk and resilience factors on multiple levels (i.e., the individual, couple, and family level) and elucidate the role of family processes as key intermediary mechanisms of how these factors prospectively affect a wide range of psychological child outcomes. A participatory research approach ensures proper representation of families’ lived experiences. Methods: Across three data waves (each one year apart), we prospectively examine risk and resilience factors of child adjustment in LGBTQ parent families. We will assess 150 LGBTQ parent families (including single parents) at each wave through online questionnaires stratified by three child age cohorts (early childhood; middle childhood; adolescence). From a focal sample, we obtain observational data of dyadic and triadic family processes using standardized procedures. Analyses will be conducted by non-linear machine learning models. Innovation: The RALF Study is to our knowledge the first prospective study globally to comprehensively assess family functioning and risk and resilience factors of children living in LGBTQ parent families using a multi-method, multi-rater, and intersectional approach. Intersectionality, a leading perspective in LGBTQ health research, requires novel statistical techniques that model complex interactions between variables. We will thus introduce non-linear machine learning techniques to the field. Our community-based participatory research framework will actively involve community members and stakeholders throughout the research process. This includes easily accessible dissemination strategies (e.g., the open access data explorer ExploRALF) to root study results in the community they serve. Primary researchers involved: Martina Zemp (PI): Professor of Clinical Child and Adolescent Psychology (Department of Clinical and Health Psychology, University of Vienna), & Magdalena Siegel (Co-PI): PhD student, future postdoc researcher in this project (same affiliation).