The UsingContexts() function returns the current default context(s).

$\mathrm{with}\left(\mathrm{Units}\right)\:$

Automatically loading the Units[Simple] subpackage

$\mathrm{UsingContexts}\left(\right)$

$\mathrm{UseContexts}\left('\mathrm{troy}'\,'\mathrm{US\_survey}'\right)$

$\mathrm{UsingContexts}\left(\right)$

$\mathrm{troy},\mathrm{US\_survey}$