  Observational evidence has been mounting for the existence of intermediate
mass black holes (IMBHs, 10^2-10^5 Msun), but observing them at all, much less
constraining their masses, is very challenging. In one theorized formation
channel, IMBHs are the seeds for supermassive black holes in the early
universe. As a result, IMBHs are predicted to exist in the local universe in
dwarf galaxies, as well as wandering in more massive galaxy halos. However,
these environments are not conducive to the accretion events or dynamical
signatures that allow us to detect IMBHs. The Laser Interferometer Space
Antenna (LISA) will demystify IMBHs by detecting the mergers of these objects
out to extremely high redshifts, while measuring their masses with extremely
high precision. These observations of merging IMBHs will allow us to constrain
the formation mechanism and subsequent evolution of massive black holes, from
the 'dark ages' to the present day, and reveal the role that IMBHs play in
hierarchical galaxy evolution.
