The azimuthal anisotropies of particle yields observed in relativistic heavy ion collisions have been traditionally considered as a strong evidence of the formation on a deconfined quark-gluon plasma produced in these collisions. However multiple recent measurements in $pp$ and $p$/D/He+A collisions show similar features as those observed in A+A Collisions, indicating the possibility of the production of such a deconfined medium in smaller collision systems. In this talk I will present a comprehensive summary of these measurements in small systems. It includes measurements of identified and inclusive two-particle correlations in $\Delta\phi$ and $\Delta\eta$, with different procedures used to subtract the dijet contributions, as well as measurements of multi-particle cumulants $c_{2--8}$. The traditional cumulant measurements confirm presence of collective phenomena in $p$+A collisions, but are biased by non-flow correlations and are not able to provide evidence for collectivity in $pp$ collisions. To address this, a new sub-event cumulant method that further suppresses the contribution non-flow effects was developed, whose measurements will also be discussed.

Collectivity in high energy collisions