The technical challenges of the Large Hadron Collider.

The Large Hadron Collider (LHC) is a 27km circumference hadron collider, built at CERN to explore the energy frontier of particle physics. Approved in 1994, it was commissioned and began operation for data taking in 2009. The design and construction of the LHC presented many design, engineering and logistical challenges which involved pushing a number of technologies well beyond their level at the time. Since the start-up of the machine, there has been a very successful 3-year run with an impressive amount of data delivered to the LHC experiments. With an increasingly large stored energy in the beam, the operation of the machine itself presented many challenges and some of these will be discussed. Finally, the planning for the next 20 years has been outlined with progressive upgrades of the machine, first to nominal energy, then to progressively higher collision rates. At each stage the technical challenges are illustrated with a few examples.