  Here we provide a review of Mira variables, their basic properties, and
Period-Luminosity Relations with an emphasis on their role in measuring the
Hubble Constant. The usage of multiple independent distance indicators and
methods is crucial to cross-checking systematic uncertainties in distance
measurements and in reinforcing previous findings of the Hubble tension. To
this end, Mira variables serve as an alternative Type Ia Supernova calibrator
to the more commonly-used Cepheid variables or Tip of the Red Giant Branch
method. They also have the potential to expand the number of local SN Ia
calibrators by calibrating previously-inaccessible SNe Ia. Short-period ($P
\lesssim 400$ d) O-rich Miras are a ubiquitous older population that can reach
galaxies not hosting the younger Cepheids variables or out of reach to the old
but fainter Tip of the Red Giant Branch. With the current and upcoming focus on
infrared observations, Miras, which can be discovered and characterized using
exclusively near-infrared and infrared observations, will be particularly
useful in obtaining distances to astrophysical objects. Long-period Miras ($P
\gtrsim 400$ d) are highly luminous variables that have the potential to
measure $H_0$ directly, excluding Type Ia SNe altogether in the distance
ladder.
