Abstract Background Valid measures of the well-being of older people are important for the evaluation of health and social care services. The nine-item Well-being of Older People measure (WOOP) was based on a novel framework derived from a recent Q-methodology study, and was developed to capture a comprehensive set of well-being domains relevant to older people, as identified by themselves. This study introduces the WOOP and describes the qualitative assessment of its feasibility and content validity. Methods Between December 2017 and January 2018, a sampling agency retrieved data from 269 adults aged 65 years and older in the Netherlands. Using an online survey, participants were asked to complete the WOOP and to indicate the importance of each item to their well-being. Open-ended questions were used to collect information about participants’ own definition of well-being, their interpretation of the items of the WOOP, and their assessment of the descriptions and response options provided with each item. Data were analysed using inductive content analysis with the software package ATLAS.ti. Results The WOOP closely resembled respondents’ own description of what well-being means to them. The majority of the respondents reported no important well-being aspects to be missing from the WOOP, and indicated all WOOP items to be at least ‘reasonably important’ to their well-being. Many linked the WOOP items to well-being aspects as intended, and only a few had suggestions for improving the items’ descriptions and response options. Conclusions Given these results, all nine items were retained, and no items were added to the measure. Based on respondents’ feedback, minor changes were made to the wording of some descriptions and response options of items. Concluding, the feasibility and content validity of the WOOP seem satisfactory. Further validation of this new measure is required, in different health and social care settings and among subgroups of older people with potentially different views on what constitutes ...