  We demonstrate that the concept of moir\'e flat bands can be generalized to
achieve electronic band engineering in all three spatial dimensions. For many
two dimensional van der Waals materials, twisting two adjacent layers with
respect to each other leads to flat electronic bands in the two corresponding
spatial directions -- a notion sometimes referred to as twistronics as it
enables a wealth of physical phenomena. Within this two dimensional plane,
large moir\'e patterns of nanometer size form. The basic concept we propose
here is to stack multiple twisted layers on top of each other in a predefined
pattern. If the pattern is chosen such that with respect to the stacking
direction of layers, the large spatial moir\'e features are spatially shifted
from one twisted layer to the next, the system exhibits twist angle controlled
flat bands in all of the three spatial directions. With this, our proposal
extends the use of twistronic to three dimensions. We exemplify the general
concept by considering graphitic systems, boron nitride and WSe$_2$ as
candidate materials, but the approach is applicable to any two-dimensional van
der Waals material. For hexagonal boron nitride we develope an ab initio fitted
tight binding model that captures the corresponding three dimensional
low-energy electronic structure. We outline that interesting three dimensional
correlated phases of matter can be induced and controlled following this route,
including quantum magnets and unconventional superconducting states.
