In his Ph.D thesis, John Tate attached local constants with characters of a
non-Archimedean local field of characteristic zero. Robert Langlands proved the
existence theorem of non-abelian local constants of higher dimensional complex
local Galois representations. Later Helmut Koch summarized Langlands' strategy
and gave shorter version (group theoretic) of Langlands' proof. The Brauer
induction formula plays a very crucial role in the Langlands' proof. Robert
Boltje gives a canonical version of the Brauer induction formula. In this
paper, we review the Langlands' strategy via Boltje's canonical Brauer
induction formula. After that we also review properties of local constants,
some applications and open problems.Comment: 54 page