Volunteering by immigrants provides dual a contribution: To civil society, immigrant volunteers can add an untapped human and social capital, social diversity and multiculturalism; to the immigrant, volunteering offers cultural, economic, and social benefits in their integration efforts. Yet, we need a more multidimensional probing of the term ‘immigrant volunteering’, because the multiplicity of migration generations requires questioning who is an ‘immigrant’, and formal volunteering does not capture the full array of unpaid work done by immigrants, suggesting the need to consider informal volunteering. By comparing formal and informal volunteering behavior of three immigrant groups (second-generation, generation 1.5, first-generation), we reflect on several distinctions and overlooked dimensions that might better explain whether and why immigrants withhold their volunteering. Using the 2014 wave of the German Survey on Volunteering, our findings indicate variation on formal and informal volunteering between the migration groups: differences are greater in formal volunteering, but smaller when we consider informal volunteering. Citizenship status and language proficiency also play a role. Implications of these findings are discussed.