In spite of the large research interest in older adults’ wellbeing, a theory of older adult’s wellbeing as such is still lacking. I present the outline of such a theory, determining its scope and premises and suggesting avenues for its further development and related empirical research. I assume that wellbeing is a complex and dynamic phenomenon, depending on a subtle interplay between several different factors. Older adults tend to combine and value these factors differently from other age groups, and this should be reflected by a domain-specific wellbeing theory. I argue more specifically that dispositional properties are less important to older adults’ wellbeing; that vulnerability is a second-order disposition, and that this explains why it does not seem to impede wellbeing; that hedonic adaptation takes very different forms, not least in older adults, and that it should be assessed in a correspondingly differentiated manner; that cognition and cognitive impairment can play very different, both positive and negative, roles depending on the context; and that notions like flourishing need modification, and are actually modified in wellbeing assessments and self-assessments.