  The presence of correlations between particles significantly separated in
pseudorapidity in proton-proton and proton-nucleus collisions has raised
questions about whether collective effects are observed in small collision
systems as well as in heavy-ion collisions. The quantification of these
long-range correlations by $v_n$ coefficients is of particular interest. A
selection of the latest $v_n$ measurements is presented, including results from
the recent $d$+Au beam energy scan at RHIC where a significant non-zero $v_2$
is measured down to low center-of-mass energies ($\sqrt{s_{\rm{NN}}}$ = 39
GeV). Results from a collision system scan - comprising $p$+Au, $d$+Au, and
$^3$He+Au collisions - are also shown to address the role of the initial
nuclear geometry in the final state anisotropy. Finally, the challenge of
measuring multi-particle cumulants, particularly $c_2\{4\}$, in $p$+$p$
collisions is discussed, and new methods for reducing the effects of non-flow
are shown to produce a more robust measurement of $v_2\{4\}$ in $p$+$p$
collisions.
