An overview of quantum-mechanical methods to generate cross-section data for electron collisions with atoms and molecules is presented. Particular emphasis is placed on the time-independent close-coupling approach, since it is particularly suitable for low-energy collisions and also allows for systematic improvements as well as uncertainty estimates. The basic ideas are illustrated with examples for electron collisions with argon atoms and methane. For many atomic systems, such as e-Ar collisions, highly reliable cross sections can now be computed with quantified uncertainties. On the other hand, while electron collision calculations with molecules do provide key input data for plasma models, the methods, and computer codes presently used require further development to make these inputs robust.