What are we, and everything around us, made of?  How are we held together without breaking apart? Science has made tremendous progress in the last one hundred years or so in establishing a convincing picture of nature, its most basic elements and how they interact with each other. The understanding we have developed is very effective and can describe essentially all man-made experiments and studies, including those that probe the deepest questions such as "what gives mass to everything". The answer is inextricably connected to what the vacuum really is. The latter question is now being addressed by the gigantic experiments of particle physics at the CERN Large Hadron  Collider. In this talk I will describe how these experiments study matter and the forces that act on matter, and then turn to the question of whether space in the absence of matter is empty -- or not.

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