Cheese is made by coagulating or clotting milk. This is achieved by first acidifying the milk with a bacterial culture and then adding rennet, an enzyme, to coagulate the milk, separating it into curds, the solid and liquid (whey) products.  There are hundreds of types of cheeses related to different flavours, different types of milks, different types of processes involved, different consistency etc soft, hard.

 If cheese is made from rennet of pig or animal which has not been slaughtered in the Islamic way or from genetically modified rennet from a similar animal then it will not be Halal.