Neutrino astronomy has reached a watershed with the construction and commissioning of the cubic-kilometer IceCube neutrino detector and its low energy extension DeepCore. The instrument detects neutrinos over a wide energy range: from 10 GeV atmospheric neutrinos to 1010 GeV cosmogenic neutrinos.Topics for discussion are: the scientific rational for building a kilometer-scale neutrino detector, the challenges in building IceCube and the present detector performance, initial results based on the more than 300,000 neutrino events recorded during construction. We will emphasize the measurement of the high-energy atmospheric neutrino spectrum extending to PeV energy and discuss IceCube's potential for neutrino physics and for identifying the particle nature of dark matter. Furthermore, we discuss the search for the still enigmatic sources of the galactic and extragalactic cosmic rays. Finally, we will discuss how the first data taken with the completed detector have revealed strong evidence for a flux of extraterrestrial neutrinos.