Chimneys are regularly subjected to intense heat, windblown rain, freezing temperatures, and other environmental hazards. The chimney cap is the most exposed portion. Reasons why chimney caps fail are addressed. There are four main problems: extreme exposure to water absorption and collection; using ordinary bricklaying mortar for the cap; tapering of mortar along the perimeter; and the fact that the cap may not be insulated from the flue liner. All of these problems allow water to enter the cap, which deteriorates over time, subsequently leading to water flow into the chimney. Alternative cap designs are outlined and illustrated. A recommended cap is made of reinforced concrete at least 2 inches thick. The construction of the cap is detailed.