Manifestations of hybrid threats are in the news. The general public has become aware, maybe not of the full concept, but certainly of some of the more striking incidents. Institutions like NATO and the EU write policy papers and organize symposia and workshops to discuss it. Government officials warn us about it. But what exactly is this hodgepodge of little green men, disinformation campaigns, online recruiting of jihadists, cyber-attacks, strategic acquisitions, meddling with elections, etc.? TNO and HCSS have joined forces to explain to the interested lay person what hybrid threats are. In a small booklet the What ( what is it?), the Why (why should we care?), and the How (how should we deal with its challenges?) of everything hybrid is discussed. A number of key issues and themes are introduced, and illustrated by examples. But be warned: the booklet does not provide final answers. Not because we want to keep the answers to ourselves, or that these answers are too complicated to explain, but for the simple reason that the very nature of the phenomenon itself makes it impossible to pinpoint what hybrid threats exactly are.