A Tudor bonnet (also referred to as a doctor's bonnet or round cap) is a traditional soft-crowned, round-brimmed cap, with a tassel hanging from a cord encircling the puggaree of the hat. As the name suggests, the Tudor bonnet was popularly worn in England and elsewhere during Tudor times.
In some educational establishments, or some faculties of some educational establishments, a mortarboard is worn instead.
It is worn as traditional clothing with gowns most especially livery and burgess guilds officers as suitable headwear.
They can be made of velvet or cloth, usually black but can be produced in other colours. The cord and tassel can come in a variety of colours; gold is common in academic caps but in Oxford, a black ribbon is used instead.