  EL CVn-type binaries contain an A-type dwarf star and a very low mass ($\sim
0.2M_\odot$) helium white dwarf precursor (pre-He WD). Recent surveys and
observations have discovered dozens of them, and showed that some pre-He WDs
have multi-periodic pulsations, opening up the possibility of using
asteroseismology to study the interior structure of these stars. We have
studied the formation of EL CVn-type binaries to understand the physics of
their formation and give the properties and the space density of this
population of stars in the Galaxy. We use a simple analysis to show that EL CVn
binaries cannot be produced by rapid common envelope evolution because this
process leads to merging of the components when a giant has such a low-mass
core. We find that EL CVn-type binaries can be produced by long-term stable
mass transfer between low-mass stars in close binary systems. We have
comprehensively studied this formation channel and the characteristics of the
resulting population of EL CVn-type binaries from more than 65,000 runs of
binary evolution with primary star masses between 0.9 and $2.0M_\odot$ and
assuming composition appropriate for Population I stars. The theoretical
evolutionary tracks, mass ratios and the WD mass-period ($M_{\rm WD}-P$)
relation are generally in agreement with observations. We conclude that many
more EL CVn-type binaries remain to be discovered and that these binaries will
be predominantly low-mass systems in old stellar populations.
