Prevention is shifting from focusing primarily on crisis responses to housing and homelessness and asking 'what can we do to stop people from becoming homeless in the first place? It means understanding the big picture and the inflows into homelessness. It means working upstream to stop homelessness from occurring, providing early intervention support and quickly re-housing if housing instability looks inevitable. Prevention requires a big system response. This toolkit focuses on how communities and housing professionals can integrate upstream and preventative thinking into their current approach.