  The physics of two-dimensional (2D) materials and heterostructures based on
such crystals has been developing extremely fast. With new 2D materials, truly
2D physics has started to appear (e.g. absence of long-range order, 2D
excitons, commensurate-incommensurate transition, etc). Novel heterostructure
devices are also starting to appear - tunneling transistors, resonant tunneling
diodes, light emitting diodes, etc. Composed from individual 2D crystals, such
devices utilize the properties of those crystals to create functionalities that
are not accessible to us in other heterostructures. We review the properties of
novel 2D crystals and how their properties are used in new heterostructure
devices.
