Quantum-dot cellular automata (QCA) are a transistorless approach to carrying out digital computing with nanoscale devices. The QCA cell is a structure comprising a small number of locations called dots, which can hold electrons, and the arrangement of charge among these dots represents binary information. Because no electric current flows from cell to cell, the QCA approach constitutes a radical departure from conventional electronics, one which may prove more suitable for computing at the nanometer and molecular scales.