Autophagy　starts　with　the　initiation　and　nucleation　of　isolation　membranes,　which　further　expand　and　seal　to　form　autophagosomes.　The　regulation　of　isolation　membrane　closure　remains　poorly　understood.　CK1　delta　is　a　member　of　the　casein　kinase　I　family　of　serine/threonine　specific　kinases.　Although　CK1　delta　is　reported　to　be　involved　in　various　cellular　processes,　its　role　in　autophagy　is　unknown.　Here,　we　show　that　CK1　delta　regulates　the　progression　of　autophagy　from　the　formation　of　isolation　membranes　to　autophagosome　closure,　and　is　essential　for　macroautophagy.　CK1　delta　depletion　results　in　impaired　autophagy　flux　and　the　accumulation　of　unsealed　isolation　membranes.　The　association　of　LC3　with　ATG9A,　ATG14L,　and　ATG16L1　was　found　to　be　increased　in　CK1　delta-depleted　cells.　The　role　of　CK1　delta　in　autophagosome　completion　appears　to　be　conserved　between　yeasts　and　humans.　Our　data　reveal　a　key　role　for　CK1　delta/Hrr25　in　autophagosome　completion.