  Alfv\'enic fluctuations are very common features in the solar wind and are
found especially within the main portion of fast wind streams while the slow
wind usually is less Alfv\'enic and more variable. In general, fast and slow
wind show many differences which span from the large scale structure to small
scale phenomena including also a different turbulent behaviour. Recent studies,
however, have shown that even slow wind can be sometimes highly Alfv\'enic with
fluctuations as large as those of the fast wind. The present study is devoted
to present many facets of this Alfv\'enic slow solar wind including for example
the study of the source regions and their connection to coronal structures,
large-scale properties and micro-scale phenomena and also impact on the
spectral features. This study will be conducted performing a comparative
analysis with the typical slow wind and with the fast wind. It has been found
that the fast wind and the Alfv\'enic slow wind share common characteristics,
probably attributable to their similar solar origin, i.e. coronal-hole solar
wind. Given these similarities, it is suggested that in the Alfv\'enic slow
wind a major role is played by the super-radial expansion responsible for the
lower velocity. Relevant implications of these new findings for the upcoming
Solar Orbiter and Solar Probe Plus missions, and more in general for turbulence
measurements close to the Sun, will be discussed.
