  ALMA will become fully operational in a few years and open a new window on
primordial galaxies. The mm and submm domain is privileged, since the peak of
dust emission between 60 and 100 microns is redshifted there for z= 5-10, and
the continuum benefits from a negative K-correction. At least 100 times more
sources than with present instruments could be discovered, so that more normal
galaxies, with lower luminosities than huge starbursts and quasars will be
surveyed. The high spatial resolution will suppress the confusion, which
plagues today single dish bolometer surveys. Several CO lines detected in
broad-band receivers will determine the redshift of objects too obscured to be
seen in the optical. With the present instrumentation, only the most massive
and gas rich objects have been detected in CO at high z, most of them being
ultra-luminous starbursts with an extremely high star formation efficiency.
However, selection biases are omni-present in this domain, and ALMA will
statistically clarify the evolution of star formation efficiency, being fully
complementary to JWST and ELTs.
