This dissertation examines the development of ethnic consciousness in Boston's Irish and Jewish communities in the late nineteenth and early twentieth centuries, focusing on several interrelated areas of analysis: religion, public service, ethnic nationalism, and popular culture. As the city's leading non-Protestant groups, Irish and Jews challenged ideas of Yankee superiority, arguing they could retain their ethnic culture and still be respected, patriotic citizens. Both groups consisted of a small middle class of businessmen and professionals and a large immigrant working class. From these factions emerged the competing voices of individuals who sought to find the best way to promote the compatibility of their religion, culture, and ethnic nationalist aspirations with American loyalties. After decades of trying to achieve full acceptance, Irish and Jews saw World War I as the ultimate test of ethnic patriotism; instead of conforming to a prescribed notion of Anglo-Protestant citizenship, they insisted on the centrality of their religion and culture to civic identity. Yet while their war service brought confidence in their rights as ethnic Americans, it did not bring total acceptance. By the 1920s, the Irish controlled local public life, but assumed a defensive posture toward the Yankee elite; Jews, meanwhile, were optimistic regarding interfaith cooperation, despite increasing antisemitism. This study expands on and moves beyond present studies of immigrant acculturation by adding a new comparative dimension. It examines the contested expressions of ethnic patriotism based on class, gender, and generation within two ethnic communities, demonstrating how ethnic groups utilized similar strategies to project a positive public image and articulate their place in society. It also shows the intersection of local, national, and international concerns in the development of ethnic consciousness. Irish and Jews created hybrid ethnic cultures rooted in religion, cultural practices, and mass consumerism that would survive for decades in the city's entrenched ethnic neighborhoods.