Secure Communities is a central program in the Obama administration’s immigration enforcement and deportation agenda. But these days, it’s also the most controversial. Last week Inspector General Charles Edwards of the Department of Homeland Security announced that his office would be opening an investigation into the federal government’s handling of the program, which sends fingerprints of anyone who’s booked in a participating local or county jail on to federal authorities who then check out people’s immigration status. The federal immigration and local law enforcement partnerships, once billed as voluntary, are now being recast as a mandatory program, and counties in California and Maryland and states like Illinois which have attempted to step out of the program have been denied.Immigration advocates contend that not only did the federal government lie to localities about the implementation of the program–this is the charge California Rep. Zoe Lofgren led with when she demanded the impending investigation–but say that the federal government does not have the authority to force localities to join them in enforcing federal immigration law.As the fight heats up, there’s plenty to catch up on. Here now, a visual primer on Secure Communities and the shape it’s taken around the country.