Aloneliness is conceptualized as the negative feelings that arise from the perception that one is not spending enough time alone. We developed and validated an assessment of aloneliness and explored its role in the links between motivations for solitude, time spent alone, and wellbeing. Studies 1 (N=643) and 2 (N=379) described the construction and validation of the Solitude and Aloneness Scale (SolAS). Study 3 (N=418) examined the role of aloneliness as a mediator of the links between motivations for solitude and wellbeing. Study 4 (N=967) explored aloneliness as a moderator of links between time alone and depressive symptoms. Cumulatively, results supported the validity and theoretical utility of aloneliness in elucidating the complex associations being solitude and wellbeing.