The discovery of superconductivity and other electronic phases in twisted bilayer graphene has led to an intensive study of similar properties in other arrangements of two dimensional materials. These systems are based on structures on scales much larger than typical inter-atomic distances (moiré structures), and they provide a fascinating connection between microscopic and mesoscopic physics.

The origin of the unusual properties of twisted bilayer graphene, still not fully understood, is reviewed, with emphasis on new effects and interactions not encountered before in condensed matter physics. The similarities and differences with other materials with complex electronic phases will be emphasized.