What is Chalav Yisrael?
Milk or dairy products are referred to as Chalav Yisrael (Israel Milk) if they were produced under constant rabbinical supervision from milking through packaging.
Milk from a kosher animal is kosher. Jewish supervision of the milk production process is the best way to ensure that milk will come from a kosher animal. Rabbinical authorities, in the Shulchan Aruch (Yoreh De’ah 115:1), decided that Jews should only consume milk produced under Jewish supervision, which is known as Chalav Yisrael.
However, there is debate over the need for Chalav Yisrael. Some rabbis, such as Rav Moshe Feinstein, argue that all milk in the United States automatically has the status of Chalav Yisrael, as the government inspects all dairy factories to assure that there is no milk from non-kosher animals.