  After a brief discussion of small and large gauge transformations and the
nature of observables, we discuss superselection sectors in gauge theories.
There are an infinity of them, classified by large gauge transformations. Gauge
theory sectors are labelled by the eigenvalues of a complete commuting set
(CCS) of these transformations.
  In QED, the standard chemical potential is one such operator generating
global U(1). There are many more given by the moments of the electric field on
the sphere at infinity. In QCD, the CCS are constructed from the two commuting
generators spanning a Cartan subalgebra.
  We show that any element of a large gauge transformation can be added to the
standard Hamiltonian as a chemical potential without changing field equations
and that in QCD, they lead to confined and deconfined phases . A speculation
about the physical meaning of these chemical potentials is also made.
  Comment: This note is based on seminars by the author. So only a limited
number of references are given, from which further literature can be traced.
  A paper is under preparation.
