The notion of solidarity, although not new to the humanitarian sector, has re-emerged in recent discussions about effective and ethical humanitarian action, particularly in contexts such as Ukraine and Myanmar where the traditional humanitarian principles have been facing certain pressures. Because solidarity appears as a good but can also involve selectivity and privilege, and because it risks continued militarism and normalization of civilians participating within that militarism, the notion of solidarity merits rich and rigorous thinking. This article explores how the notion of solidarity is being utilized by those currently re-emphasizing its importance and what it might mean in practice in today's humanitarian contexts. The article argues that if solidary action involves not only a political stance but solidary working methods, the recent calls for solidarity demand respect for the variety of principles and practices within the humanitarian ecosystem, while nevertheless upholding mutual obligations owed within that professional community – that is, within careful limits as to what is considered humanitarian action.