There are 3 arrondissements in the Isère department. The Frenchdepartments, and in other countries, are divided into arrondissements, which may be translated into English as districts (in some cases, as boroughs). The capital of an arrondissement is called a subprefecture.
If the prefecture (capital) of the department is in an arrondissement, that prefecture is the capital of the arrondissement, acting both as a prefecture and as a subprefecture.
Arrondissements are further divided into communes.