Present-day electronics employ circuits of smaller and smaller dimensions, and today the length scales are so small that the laws of physics which rule micro-cosmos, quantum mechanics, become directly important. This thesis reports on theoretical work on electron transport in different nanostructures. We have studied semiconductor quantum wells, layered materials where each layer can be only a few atomic layers thick, and transport in thin atomic wires. The layered materials have been studied semi-classically by means the so-called Bolzmann equation and Monte-Carlo techniques. The works on layered materials focused on effects of resonant scattering mechanisms on the electron transport and the feasibility to use semiconductor superlattices for generating terahertz (THz)radiation. The quantum wires were modeled by 1D Hubbard chains connected to semi-infinite leads and were treated fully quantum-mechanically via the time-dependent densityfunctional theory (TDDFT). Our TDDFT treatment appears to be able to capture complex features due to competition between correlation and disorder. The merits of the coherent-potential approximation are also analyzed for contacted chains.