SUMMARY The measurement of instrumental activities of daily living (IADL) is common in clinical practice and research into dementia. IADL are cognitively complex daily activities, such as cooking and doing finances. Their measurement is required for the diagnostic process of dementia, and also useful for the monitoring of disease progression. Since problems in IADL contribute to the disease burden of both patient and caregiver, it is a relevant outcome measure for disease-modifying and non-pharmacological interventions. Despite the widespread use of IADL instruments, an overview of its theoretical background, measurement methods, and potential sources of bias is lacking. In the current manuscript, we therefore aim to provide a selective overview of these topics.