On April 26, 1986, the #4 reactor at the Chernobyl Nuclear Power Plant in the Soviet Union suffered a severe accident which destroyed the reactor core. The reactor design and the accident sequence are reviewed in detail, using Soviet literature and information presented at the International Atomic Energy Agency Post-Accident Review Meeting in August 1986. The aspects of the design and operation which exacerbated the accident, in our view, are presented and compared to the CANDU reactor design. Key design aspects of Chernobyl examined are (in order of importance): capability of shutdown, containment and variation of void reactivity with operating state.