In particle physics, the tracking is the act of measuring the direction and magnitude of charged particles momenta. The particles entering a tracker (the device used for tracking), release part of their energy in the device: the tracker has to be finely segmented in order to be able to reconstruct with good precision where the particle passed. Since the tracking is usually made in a region where a magnetic field is present, it is possible to reconstruct part of the helix made by the particle inside the tracker (that is called track), and from the track parameters, and by knowing the mass of the particle under study (which is known by the use of particle identification), it is possible to reconstruct the actual direction and magnitude of the particle momenta. From these information the tracking of charged particles can be used to reconstruct secondary decays, this can be done for B-tagging (in experiments like CDF or at LHC) or to fully reconstruct events (like in BaBar and Belle).
In particle physics there have been many devices used for tracking as bubble chambers, multi wire proportional chambers, time projection chambers, and, with the advent of modern photolithography, the solid state trackers, also called silicon trackers.