International development, humanitarian aid, and relief are at the heart of international social work practice. They have evolved historically and globally; shaped by world markets, social and environmental forces, including natural disasters. Considering this context, the authors cluster relevant social-work theories and practices as (a) human rights perspectives and (b) ecological, feminist, and cultural theories. They discuss both micro and macro practice, with an emphasis on the latter. Case studies are presented with the overlay of relevant international conventions, guidance, and international private law. A continuum of humanitarian assistance is presented considering different countries. Guatemala is a prominent example in addition to Haiti’s massive earthquake of 2010 with recent revelations of sexual abuse and exploitation by humanitarian aid workers, post-conflict community-based practices in Afghanistan, and the largest cross-border forced migration in modern history of Iraqi, and Syrian refugees with this second group being of particular concern given their mass displacement. Capacity building as related to social work training is emphasized. This entry concludes that much remains to be accomplished with regard to capacity building among humanitarian assistance organizations so that the principles and practice strategies of international social work are institutionalized.