Abstract
PurposeNon-profit organizations (NPO) contribute significantly to the welfare of citizens and communities. Engagement in volunteering is crucial for sustaining volunteer motivation and for the effective and efficient functioning of NPO, with significant implications for society at large. Yet, literature on volunteer engagement (VE) is limited to date. Grounded on service-dominant logic, self-congruity theory and self-determination theory, this study aims to understand what motivates VE and how it may evolve into a co-creation process valuable to NPO and its stakeholders.Design/methodology/approachBased on survey data collected from 450 volunteers, working with a diverse set of NPO, a comprehensive model of drivers and outcomes of VE was empirically tested using PLS-SEM, considering the mediating role of volunteers' congruence with the core values of the NPO.FindingsThe impact of volunteers' perceived autonomy, competence and relatedness on VE and its subsequent role in volunteers' loyalty and extra-role engagement behaviors (i.e. co-development, influencing and mobilizing behaviors) were validated. Moreover, the study validates value congruence as an internalizing mediating mechanism in the engagement process, a role that has been implied but not empirically tested.Originality/valueThe study contributes to the engagement and volunteering literature, which despite an unprecedented parallel have developed almost independently, with limited reference to one another. As the nomological network of VE is still underexplored, the study extends the engagement literature to the volunteering sector, validating the key (but underexplored) role of self-determination needs and value congruence in driving VE and value co-creation behaviors. The study further adds to engagement research while addressing other actors' engagement beyond the customer-brand dyad. While adopting a seldom explored marketing perspective of VE, this study provides NPO valuable insights on how to manage and engage volunteers.

Abstract
Engagement plays a key role for most organizations. Establishing close relationships with consumers and other stakeholders - thus promoting their loyalty and participation in the value creation process - has become an element of competitive advantage. Extant literature has focused consumer-brands relationships in commercial contexts; yet, when it comes to non-commercial or non-profit contexts - where communities of decidedly engaged individuals voluntarily invest their time and energy to a cause - research is still in its infancy. This study sets out to understand how non-profit organizations (NPO) can generate a sense of engagement among volunteers and which volunteers' behaviours - associated with that psychological state - entice value co-creation with NPO. Group interviews were carried out with volunteers to gain insights on drivers and outcomes of Volunteer Engagement (VE). Value congruence between volunteers and NPO, a sense of community, as well as perceptions of competence and autonomy, were identified as drivers of VE. The study further validated the impact of VE not only on somewhat predictable outcomes, such as NPO loyalty and advocacy, but also on the co-creation of value with NPO through the recruitment of new volunteers and the development of new ideas for service innovation.