Since every total order is a
lattice order, and the real field R is a totally ordered field, it is a lattice-ordered field.
In 1956 Birkhoff and Pierce raised the question of whether R can be made into a
lattice-ordered field in any other way. In this paper we answer their question
affirmatively by showing that there are, in fact, 2c such orderings, where c is the
cardinal of R.