It's called Dazhao Si in Mandarin, Jokhang Temple in English. It's a 1350 years old Tibetan Buddhism temple, the most highest reputable lama temple in Tibet. The Tibetans say that "First came the Jokhang Temple, then Lhasa City after." It's now the political & religious palace of Tibet. The most important religious activities are usually held there, such as the Golden Urn. Also, the Buddha Statue at age 12 is in this temple.