Quantifying messenger RNA (mRNA) translation at the single-molecule level. Many mechanistic details of mRNA translation can now be measured in living cells. (Top) The rates of ribosome initiation, nascent chain elongation, ribosome stalling, and translation termination can be measured, as can the density of ribosomes within polysomes. (Bottom) Polysome shape, higher-order structure, mobility, and localization can also be measured.