In these lectures I shall discuss the status of the determination
of the three cosmological parameters
which enter the Einstein equation and govern geometry
and evolution of space-time of the Universe:
the Hubble constant *H*_{0},
the mass density parameter and
the cosmological constant
.

Among the three parameters,
the Hubble constant is the dimensionfull quantity which sets the
basic size and age of the Universe. The perennial effort
to determine *H*_{0} dates back to
Hubble (1925)
and has a long history of disconcordance. Recent progress has
done much to resolve the long-standing
discrepancy concerning the extragalactic distance scale, but there are
some newly revealed uncertainties in the distance scale
within the Milky Way. The emphasis in this lecture is on discussion of
these uncertainties.

The mass density parameter directly determines the formation of cosmic structure. So, as our understanding of the cosmic structure formation is tightened, we should have a convergence of the parameter. An important test is to examine whether the parameter extracted from cosmic structure formation agrees with the value estimated in more direct ways. This gives an essential verification for the theory of structure formation.

The third important parameter in the Friedmann universe is the cosmological constant . We now have some evidence for a non-zero which, if confirmed, would have most profound implications for fundamental physics. This lecture will focus on the strength of this `evidence'.

We take the normalisation

for the flat curvature, where
=
/
3*H*^{2}_{0} with
the constant entering in the
Einstein equation.
The case with = 1 and
= 0 is referred to as
the Einstein-de Sitter (EdS) universe.
We often use distance modulus

instead of the distance *d*_{L}. For conciseness, we shall
omit the units
for the Hubble constant, (km s^{-1} Mpc^{-1}).

After the Summer Institute there appeared several important papers on the distance scale. I try to incorporate these results in this article.