Integrated Access and Backhaul (IAB) allows using wireless backhaul to connect small cells and avoid wiring clutter. IAB nodes terminate the gNB-DU and support UE functionality towards the IAB donor. The IAB donor terminates the gNB-CU and lower layers for the IAB node. Backhaul Adaptation Protocol (BAP) routes packets across the backhaul topology using routing IDs. IP addresses for F1 and OAM are discovered for IAB nodes. Signaling and user plane traffic is mapped to backhaul RLC channels. Open issues in Rel-16 include BAP specification and topology adaptation procedures. Rel-17 may address inter-donor migration and topological redundancy.