The electric and magnetic fields are vector fields, which means that one has to specify both their strengths and their directions. There also exist scalar fields, specified entirely by their strength. One of them is the Higgs field, whose oscillation corresponds to the Higgs boson. There is, almost certainly, at least one more scalar field. That is the field responsible for inflation, called the inflaton field. In this chapter I describe scalar fields at the classical level, and in the next I include quantum physics. I use natural units.