A key design consideration of ALICE is the ability to study QCD and quark (de)confinement under these extreme conditions. This is done by using particles, created inside the hot volume as it expands and cools down, that live long enough to reach the sensitive detector layers situated around the interaction region. ALICE's physics programme relies on being able to identify all of them, i.e. to determine if they are electrons, photons, pions, etc. and to determine their charge. This involves making the most of the (sometimes slightly) different ways that particles interact with matter.