New Season

Yes, each season you need to do placement matches. Your placement matches may match you approximately against people of your perceived skill level due to last season's play, but you will get a chance each season to start a little higher (or lower, depending on those games) with new placement matches. It's been stated that preseason matches will count in some way toward your placement matches though, so if you do well in preseason in ranked, you may not find yourself set lower once the new season rolls out. Hope this helps!