Envelopes of holomorphy and holomorphic discs

Extension of analytic functions of one variable led to the notion of
Riemann surfaces and has applications to many branches of mathematics.
After a brief recollection I will focus on the effect in several
complex variables which made the multi-dimensional theory
geometric from the beginning and led to the notion of Stein manifolds
and envelopes of holomorphy.
I will describe a new construction of envelopes of holomorphy of
domains in terms of equivalence classes of analytic discs.
The construction is purely geometric and does not refer to the
set of analytic functions in the domain.
Several geometric corollaries will be discussed.