Kommittédirektiv starts a public inquiry, SOU
What The Government's assignment that starts a public inquiry (statlig utredning) and decides what it is to look at and when it is to be finished.
Who The Government, through the responsible ministry, writes the terms of reference (kommittédirektiv), as the ones politically responsible for which issues are to be looked into.
How You can read the terms of reference on regeringen.se to see in advance which issues are about to be investigated.