  The Hubble constant Ho describes not only the expansion of local space at
redshift z ~ 0, but is also a fundamental parameter determining the evolution
of the universe. Recent measurements of Ho anchored on Cepheid observations
have reached a precision of several percent. However, this problem is so
important that confirmation from several methods is needed to better constrain
Ho and, with it, dark energy and the curvature of space. A particularly direct
method involves the determination of distances to local galaxies far enough to
be part of the Hubble flow through water vapor (H2O) masers orbiting nuclear
supermassive black holes. The goal of this article is to describe the relevance
of Ho with respect to fundamental cosmological questions and to summarize
recent progress of the the `Megamaser Cosmology Project' (MCP) related to the
Hubble constant.
