This article is from the Hanggliding and Paragliding FAQ, by Joao Geada with numerous contributions by others.
Hanggliders can be launched, flown and landed in winds from zero
to about 30 mph safely. When winds get above about 40 mph, the
associated turbulence makes all aspects of flight substantially less
comfortable. Generally, ideal winds for launching and landing are from
5 to 20 mph depending on the flying site. Wind speed is less important
in flight since the pilot controls the air speed of the glider
whatever the wind speed may be.