A full understanding of nineteenth century Irish America requires close examination of emigration as well as immigration. Knowledge of Irish pre-emigration experiences is a key to making sense of their post-emigration lives. This work analyzes the regional origins, the migration and settlement patterns, and the work and associational life of the Catholic Irish in Brooklyn between 1850 and 1900. Over this pivotal half century, the Brooklyn Irish developed a rich associational life which included temperance, Irish nationalism, land reform and Gaelic language and athletic leagues. This era marked the emergence of a more diverse, mature Irish-Catholic community, a community which responded in a new ways to a variety of internal and external challenges. To a degree, the flowering of Irish associational life represented a reaction to the depersonalization associated with American industrialization. However, it also reflected the changing cultural norms of many post-famine immigrants. Unlike their pre-1870 predecessors, these newcomers were often more modern in outlook - more committed to Irish nationhood, less impoverished, better educated and more devout. Consequently, post-1870 immigrants tended to be over-represented in the ranks of associations dedicated to Irish nationalism, Irish temperance, trade unionism, and cultural revivalism throughout Kings County. Unsurprisingly, over 70 of Brooklyn's 96 Catholic churches in 1901 were built after July 1, 1870. The internal diversity of the Brooklyn Irish was extensive. The opportunities and experiences of some Irish differed markedly from those experienced by others. Gender, county of origin and skill level all served as factors in post-emigration success. Moreover, generation was especially pronounced as a socioeconomic agent in Brooklyn. Economic prospects for the Irish-born remained as poor in Brooklyn as anywhere in the nation, but improved more rapidly for the American-born Irish then anyone might realistically have considered possible. Increased opportunities for land ownership seemed to support the socioeconomic prospects of thrifty Irishmen, but occupational mobility strongly favored the second generation, more so than in other locales. Why do both popular and scholarly accounts tend to portray all nineteenth century Irish Americans as either an undifferentiated mass of unskilled proletarians or as nouveau riche "lace curtain" aristocrats when significant variation clearly existed? In Philadelphia, Detroit and Brooklyn, at least 30 percent of Irish-born male workers in 1880 could be classified as "skilled craftsmen." In five other major cities, from San Francisco to Providence, the corresponding figure was roughly one-fifth in the same census year. Meanwhile, the Brooklyn Irish displayed a curious pattern of halting socioeconomic progress among foreign-born men (55% nonskilled in 1850, 51% nonskilled in 1900) alongside impressive progress for their American-born sons (35% nonskilled in 1880, 22% nonskilled in 1900). Irish American socio-economic mobility paled in comparison to that of their German peers, especially among the foreign born. Their intra-urban geographic mobility patterns differed as well. Irish Americans, in Brooklyn and other Northeastern and Midwestern cities, tended to move out of the older core wards as soon as they enjoyed a degree of economic success. German Americans, conversely, seem to have reinvested their new wealth in "a nicer house in the old neighborhood." Germans tended to separate themselves, whether they lived in the tenement districts of New York's Germantown and Brooklyn's Williamsburg, or the single-family homes of Riverdale just south of the Bronx. By 1890, the Irish were virtually ubiquitous, inhabiting all areas and all housing types of Brooklyn.