Substantial progress has been made towards bothunderstanding and control of internal transport barriers (ITBs) onDIII-D, resulting in the discovery of a new sustained high performanceoperating mode termed the quiescent double barrier (QDB) regime. TheQDB regime combines core transport barriers with a quiescent ELM-freeH mode edge (termed QH mode), giving rise to separate (double) coreand edge transport barriers. The core and edge barriers are mutuallycompatible and do not merge, resulting in broad core profiles with anedge pedestal. The QH mode edge is characterized by ELM-free behaviourwith continuous multiharmonic MHD activity in the pedestal region andhas provided density and radiated power control for longer than 3.5 s (25τE)with divertor pumping. QDB plasmas are long pulse high performancecandidates, having maintained a βNH89 product of 7 for five energyconfinement times (Ti⩽16 keV, βN⩽2.9, H89⩽2.4, τE⩽150 ms, DDneutron rate Sn⩽4×1015 s-1). The QDB regime has only been obtainedin counter-NBI discharges (injection antiparallel to the plasma current)with divertor pumping. Other results include successful expansion ofthe ITB radius using (separately) both impurity injection andcounter-NBI, and the formation of ITBs in the electron thermal channelusing both ECH and strong negative central shear (NCS) at highpower. These results are interpreted within a theoretical framework inwhich turbulence suppression is the key to ITB formation and control,and a decrease in core turbulence is observed in all cases of ITBformation.