Informal care is a key pillar of long-term care provision across Europe and will likely play an even greater role in the future. Thus, research that enhances our understanding of caregiving experiences becomes increasingly relevant. The ENTWINE iCohort Study examines the personal, psychological, social, economic, and geographic factors that shape caregiving experiences. Here, we present the baseline cohort of the study and describe its design, recruitment methods, data collection procedures, measures, and early baseline findings. The study was conducted in nine countries: Germany, Greece, Ireland, Israel, Italy, the Netherlands, Poland, Sweden, and the United Kingdom. The study comprised a web- based longitudinal survey (baseline + 6-month follow-up) and optional weekly diary assessments, conducted separately with caregivers and care recipients. From 14 August 2020 to 31 August 2021, 1872 caregivers and 402 care recipients were enrolled at baseline. Participants were recruited via Facebook, and to a lesser extent via the study website or caregiver/patient organisations. Caregiver participants were predominantly female (87%) and primary caregivers (82%), with a median age of 55 years. A large proportion (80%) held at least post-secondary education, and two-thirds were married/partnered. Over half of the caregivers were employed (53%) and caring for a person with multiple chronic conditions (56%), and nearly three-quarters were caring for either a parent (42%) or a spouse/partner (32%). About three-quarters of care recipient participants were female (77%), not employed (74%), and had at least post-secondary education (77%), with a median age of 55 years. Over half of the care recipients were married/partnered (59%), receiving care primarily from their spouses/partners (61%), and diagnosed with multiple chronic conditions (57%). This study examining numerous potential influences on caregiving experiences provides an opportunity to better understand the multidimensional nature of these experiences. Such data could have implications for developing caregiving services and policies, and for future informal care research.