The Immigrant Spring of 2006, one of the largest campaigns for immigrant rights, led to widespread collective action to protect vulnerable communities against punitive legislation across the United States. More than a decade later, the 2006 mobilizations continue to shape immigrant community activism. This dissertation explains the factors that contributed to levels of mobilization during the spring of 2006 and their continuing influence for campaigns to protect immigrants. I analyze the emergence of the 2006 campaign at various levels of political life from the local level in the San Joaquin Valley of California to cities across California and explain movement emergence in the largest U.S. cities. I demonstrate the importance of negative conditions such as policy and repressive threats in the initiation of movements by immigrants and show the importance of organizing infrastructures for continued mobilization. I find that policy threats initiated immigrant resistance during 2006, but the resources available from previous campaigns mattered the most for future protest to protect immigrant communities.