Is it mandatory to wear Hijab?

Is it manditory for all girls to wear hijab? If they do not wear the hijab is this considered a sin? 

The Quran and Sunnah both direct women to cover themselves and avoid displaying their adornments in front of ?strangers? (non-mahram men).
The Quran tells the Prophet PBUH:

“O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies. That will be better, that they should be known (as free respectable women) so as not to be annoyed. And Allâh is Ever Oft-Forgiving, Most Merciful?” [al-Ahzaab 33:59].

Allah commanded His Prophet PBUH to start by telling his wives and daughters to wear the hijab because he and his family are examples for the believing men and women, then he was to command the believing women to do likewise.

Muslim reports that the Prophet PBUH said: “There are two types of the people of Hell whom I have not seen: men with whips like the tails of cattle with which they strike the people, and women who are clothed but naked, walking with an enticing gait, with something like the humps of camels on their heads. They will not enter Paradise nor even smell its fragrance, and its fragrance can be smelled from such and such a distance”.

And Allah knows best.

Sh. Riad Ouarzazi