Relations between Mexico and the United States are composed of numerous paradoxes related to the two countries’ geographical vicinity and common history. Their bilateral relationship has a certain number of critical stakes, including trade, border security and drug traffic, and particularly migration. Mexican immigration towards the United has been a fundamental parameter in foreign policy on both sides of the border, notably since the September 11th attacks. The various American and Mexican Presidents have progressively dealt with this problem through the co-responsibility principle, as Mexico wavered between a longing for sovereignty and economic reliance on its Northern neighbour. Reform plans of the United States’ immigration policy have shed light on two aspects in this bilateral relationship: on the one hand, immigration is essentially linked to global security and economic stakes ; on the other hand, the failure of this reform has led to a de-federalisation process in the migration and foreign policy.