  After close to 20 years of preparation, the dedicated heavy ion experiment
ALICE took first data at the CERN LHC accelerator with proton collisions at the
end of 2009 and with lead nuclei at the end of 2010. After a short introduction
into the physics of ultra-relativistic heavy ion collisions, this article
recalls the main design choices made for the detector and summarizes the
initial operation and performance of ALICE. Physics results from this first
year of operation concentrate on characterizing the global properties of
typical, average collisions, both in pp and nucleus-nucleus reactions, in the
new energy regime of LHC. The pp results differ, to a varying degree, from most
QCD inspired phenomenological models and provide the input needed to fine-tune
their parameters. First results from Pb-Pb are broadly consistent with
expectations based on lower energy data, indicating that high density matter
created at LHC, while much hotter and larger, still behaves like a very
strongly interacting, almost perfect liquid.
