Am I allowed to sublet my apartment, for example on Airbnb?

No, not without your landlord's written consent. For residential premises, any subletting or assignment of the lease is prohibited, except with the lessor's written consent by deed of certain date, or unless the contract stipulates otherwise (art. 39). Occupation of the premises by a third party for more than three months is, moreover, treated as a sublet (art. 39).

And tourist rentals like Airbnb? They are affected on two counts. On the one hand, short-term rentals fall under another law (Law 80-14 on tourist accommodation) and not under residential leases (art. 1). On the other hand, subletting without consent constitutes an illegal sublet.

The consequences are severe (art. 43):

• the subtenant is regarded as an occupant without right or title;
• the lessor may apply to the interim relief judge to have both the occupant and you yourself evicted;
• the sublease contract and your original lease are automatically terminated as soon as the notice is ordered.

Worth knowing for professional premises: for professional premises, the lessor cannot object to a full sublet if the activity remains the same or similar (art. 40), but any partial sublet there is void (art. 41).