Class I

Class I may refer to:
 * Class I antiarrhythmic
 * Class I electrical appliance, a device constructed according to electrical grounding specifications in the IEC 60536-2 standard
 * Class I bacteriocin, a type of toxin produced by some bacteria
 * Class I biosafety cabinet
 * Class I laser, a type of eye-safe laser defined in the ANSI Z136 standard
 * Class I rail carrier, a type of major freight railroad company in Canada
 * Class I railroad, a type of major freight railroad company in the United States