  The present rate of the expansion of our Universe, the Hubble constant, can
be predicted from the cosmological model using measurements of the early
Universe, or more directly measured from the late Universe. But as these
measurements improved, a surprising disagreement between the two appeared. In
2019, a number of independent measurements of the late Universe using different
methods and data provided consistent results making the discrepancy with the
early Universe predictions increasingly hard to ignore. We review key advances
realized by 2019:
  -- The local or late Universe measurement of the Hubble constant improved
from 10% uncertainty twenty years ago to under 2% by the end of 2019.
  -- In 2019, multiple independent teams presented measurements with different
methods and different calibrations to produce consistent results.
  -- These late Universe estimations disagree at 4$\sigma$ to 6$\sigma$ with
predictions made from the Cosmic Microwave Background in conjunction with the
standard cosmological model, a disagreement that is hard to explain or ignore.
