What is the difference between ICE and DEA?

ICE is Immigrations and Customs Enforcement. They mostly deal with illegal immigrants and any problems involving US borders.

DEA is Drug Enforcment Administration. They deal with illegal substances (drugs) and arresting drug dealers.

The biggest difference between the two is ICE is mostly inside the US and most of its agents are stationed on the US-Mexico border. While DEA is international and their agents are stationed almost everywhere illegal drugs can be found.