  The observed radial velocity of a galaxy consists of two main components: the
recession velocity caused by the smooth Hubble expansion and the peculiar
velocity resulting from the gravitational attraction of growing structures due
to matter density fluctuations. To isolate the recession velocity component and
calculate the Hubble constant, accurate measurements of true distances are
needed. The Tully-Fisher relation is an empirical correlation between the
luminosity and rotational velocity of spiral galaxies that serves as a distance
indicator to measure distances independent of redshift. The Tully-Fisher
relation has played an important role in Hubble constant measurements since its
inception. This chapter delves into the significance of the Tully-Fisher
relation in such measurements and explores its implications. We begin by
discussing the definition and historical background of the Tully-Fisher
relation. We also explore the observational evidence supporting this relation
and discuss its advantages and limitations. The chapter then focuses on the
methodology of using the Tully-Fisher relation for Hubble constant
measurements. This includes detailed explanations of calibration techniques and
biases. We emphasize the advantages of utilizing the Tully-Fisher relation,
such as its ability to provide accurate distance measurements even at
significant redshift where other methods may encounter challenges.
