Participation in the Mille Miglia is limited to makes and models of cars, manufactured between 1927 and 1957, that took part in at least of the original Mille Miglia races. These cars must be exclusively originals. Replicas, even partial ones, are not permitted to enter. 

To enter the Mille Miglia, the configuration of the car should not diverge from the original series.  Any modifications made to the car must be thoroughly documented and must have been made to the specific exemplar during the period in which it participated in an original Mille Miglia speed race. 
All cars must comply with FIA and FIVA regulations which require proper certification for participating cars.  As per international regulations, cars are required to have an FIA Heritage Certificate and/or CSAI papers and/or an FIVA (Fédération Internationale des Véhicules Anciens) Passport issued by the car’s country of origin (ANS).
As per tradition, the number of participating cars will be limited to 375.  Since the number of requests for participation in the Mille Miglia greatly exceeds the number of available places, a strict criterion of rotation of models will be applied, with precedence given as follows: 

• cars which have participated in previous original Mille Miglia speed races (documentary evidence must be provided)
• cars which have been officially entered in previous original Mille Miglia speed races (documentary evidence must be provided)
• cars with a sporting history, which have appeared on Palmares Winner’s Lists of regularity events of international significance

Under no circumstances will a car built after 1957 be permitted to enter, though cars built before 1927 may be accepted, provided models of these took part in the Mille Miglia up until 1930.