The continuing trend of miniaturizing materials in many modern technological applications has led to a strong demand for understanding the complex mechanical properties of materials at small length scales. This review focuses on the recent understanding of the size-dependent plasticity in single-crystal face-centered cubic (ficc) metals as model systems where microstructural constraints due to grain boundaries can be neglected. The small dimensions of several microns down to some tens of nanometers require sophisticated measurement approaches which are critically revisited. Size effects of the flow stresses are compared for single-crystal "wires" and single-crystalline thin films on compliant or stiff substrates. The interpretation of the results is based on recent insights on dislocation nucleation, mobility, and reactions stemming from in situ transmission electron microscopy studies or discrete dislocation dynamics simulations. Commonalities as well as differences are discussed with the attempt to explain the size effects in tensile testing at small length scales. (C) 2009 Elsevier Ltd. All rights reserved.