  With Cosmicflows-4, distances are compiled for 55,877 galaxies gathered into
38,065 groups. Eight methodologies are employed, with the largest numbers
coming from the correlations between the photometric and kinematic properties
of spiral galaxies (TF) and elliptical galaxies (FP). Supernovae that arise
from degenerate progenitors (type Ia Sne) are an important overlapping
component. Smaller contributions come from distance estimates from the surface
brightness fluctuations of elliptical galaxies and the luminosities and
expansion rates of core collapse supernovae (SNII). Cepheid period-luminosity
relation and tip of the red giant branch observations founded on local stellar
parallax measurements along with the geometric maser distance to NGC 4258
provide the absolute scaling of distances. The assembly of galaxies into groups
is an important feature of the study in facilitating overlaps between
methodologies. Merging between multiple contributions within a methodology and
between methodologies is carried out with Bayesian Markov chain Monte Carlo
procedures. The final assembly of distances is compatible with a value of the
Hubble constant of $H_0=74.6$ km s$^{-1}$ Mpc$^{-1}$ with the small statistical
error of $\pm 0.8$ km s$^{-1}$ Mpc$^{-1}$ but a large potential systematic
error of ~3 km s$^{-1}$ Mpc$^{-1}$. Peculiar velocities can be inferred from
the measured distances. The interpretation of the field of peculiar velocities
is complex because of large errors on individual components and invites
analyses beyond the scope of this study.
