You must present a valid U.S. passport or passport card in order to enter Mexico. Although documents may not be routinely checked along the land border, Mexican authorities at immigration checkpoints approximately 25 kilometers from the U.S. border will often conduct vehicle and document inspections and require valid travel documents and an entry permit or Forma Migratoria Multiple (FMM). If you enter by land and travel further than 25 kilometers into Mexico, you should stop at an immigration checkpoint to obtain an FMM, even if not explicitly directed to do so by Mexican officials. Beyond the border zone, all non-Mexican citizens must have valid immigration documents (an FMM or temporary or permanent resident card) regardless of the original place of entry. Failure to present an FMM or other valid immigration document can result in detention by immigration authorities and/or delays or missed flights because airlines may insist that a valid immigration document be obtained from Mexican immigration authorities before issuing a boarding pass.