Call them what you will - unauthorized , illegal, or undocumented - the three million immigrants in California who either entered the U.S. illegally or overstayed their visas have an impact on the state's economy and a polarizing effect on its politics. We explore the costs of illegal immigration on business, government, and the children of those who are deported, and we look at why illegal immigrants continue to find their way north in spite of formidable obstacles.