The representative body of the Region is the Regional Assembly. The Regional Assembly comprises 41 councillors elected on the direct elections.  

The Regional Assembly performs the following activities: adopts the Statute of the Region, adopts general acts in the Region's jurisdiction, nominates and absolves the President of the Region and members of the Regional Government, establishes institutions and trade societies founded by the Region, nominates members of administrative bodies of the above institutions and trade societies, makes agreements on the nomination of the directors of the institutions founded by the region, adopts the budget of the Region, performs other works defined by the Regional Statute. 

The Regional Assembly has the president and two vice presidents. The president and the vice presidents of the Regional Assembly are nominated and absolved by the Regional Assembly for the period of 4 years following the proposal of at least 10 councillors. 

Members of the Assembly solemnly swear in Croatian or in Italian: 

"I swear I will perform the rights and obligations as a member of the Assembly of the Istrian Region conscientiously and responsibly, for the economic, cultural, and social advantages of the Istrian Region, and that in performing the duties of the member of Assembly of the Istrian Region I will comply with the Statute of the Istrian Region, and protect and promote regional specifics of Istria."

The President of the Assembly reads the text of the oath, and every member, after the individual call over says: "I swear", followed by the signing of the text of the solemn oath.