Quantum-dot cellular automata (QCA) is a new computation paradigm which encodes binary information by charge configuration within a cell instead of the conventional current switches. No current flows within the cells. The columbic interaction is sufficient for computation. This revolutionary paradigm provides a possible solution for transistor-less computation at the nanoscale. QCA logic devices such as binary wires, majority gates, shift registers and fan-outs made of metal islands and small capacitors have been successfully fabricated. Experimental and theoretical research on the switching of molecular QCA cells has been underway. This thesis will focus on robustness and power dissipation in QCA circuits. The robustness of both metallic and molecular QCA circuits are studied. The power dissipation and power flow in clocked molecular QCA circuits are explored. Our results show that QCA approach is inherently robust and ultra low power dissipation is possible in QCA.