Curling is a sport that is played on a sheet of ice. Long a popular wintertime sport in northern countries such as Canada (it is the official sport of the province of Saskatchewan), Sweden, Norway, Scotland, Switzerland, Denmark, Scandinavia, and the United States, it has become global and is now played in Japan, China, New Zealand, and Korea.

Brushes sweep the ice in front of a stone during the 2005 European Curling Championship.
Curling has been a medal sport at the Winter Olympics since 1998.

Curling involves the controlled release and aim of heavy granite stones toward a target located at the other end of the ice (which, in the parlance of the sport, is called a "sheet"). Two teams of four alternately each "curls" their allotted two stones at the target. During the period of time when each team delivers the total of eight stones (called an "end"), team strategy can shift from trying to guide a stone nearest to the bulls-eye of the target (the house) to attempting to hit and remove the stones of the opposition. Depending on the number of stones nearest the target, a team can store no, one, or several points in an end. The object of curling is to outscore the opponent at the conclusion of the even number of ends (typically eight or ten).

Curling dates back centuries. It may have begun in Scotland in the sixteenth century, or even earlier, in the Netherlands. By the seventeenth century, the sport was an active part of Scottish wintertime sports. Canada's curling roots are just as deep. Indeed, the first organized sporting club in North America is the Royal Montreal Curling Club, which was founded in 1907. Just 25 years later, the first curling club was formed 1932 in the United States.

One of the unique aspects of curling concerns the playing surface. While hockey and figure skating also take place on ice, the nature of the surface is much different in curling. Because an important facet of the sport is the ability to control the movement of the curling stones, the ice is specially treated to provide friction. This is done by spraying a mist of water over the solid ice surface. The spray freezes to create a pebbled texture. In contrast, the ice surface for skating and hockey is designed to be as smooth and frictionless as possible.

As a curling match progresses, the ice pebbles are worn down by the stones. This changes the character of the ice during the match, which in turn alters the movement of the curling stones. Having to adjust to these changing conditions provides another challenge for the curlers.

The ice sheet used for a curling match is 146 ft (45.5 m) long, almost as long as a conventional hockey rink, but at 14 ft 2 in (4.3 m) it is only about a third the width of the hockey surface. Indeed, in a curling tournament such as occurs at the Olympics, three ice sheets can be placed on the ice surface. Part of the appeal of a curling tournament (called a bonspiel) is being able to see three matches in progress simultaneously.

The object of curling is to aim the stones to the center of the house. An ice sheet contains two houses, near each end (this allows play to be shifted from one end of the ice to the other end as the ice deteriorates). The bull's-eye of each house is centered by a line drawn down the middle of the sheet. Two other lines called "hog lines" are drawn at a right angle to the center line. Each hog line is located 37 ft (11.3 m) from each end of the sheet.

To score a point, a rock delivered from one end of the sheet must cross the hog line at the other end. If it does not, it is removed from play.

A granite curling stone is heavy. At a maximum of 44 lb (20 kg), it is difficult to manipulate. To deliver the stone, a curler holds onto a handle positioned on top of the rock and then, by lifting the rock slightly as they push off from a foot-stop (the "hack"), the curler slides forward and gently releases the stone. The release, which has to occur before the nearest hog line, is often accompanied by a gentle twist of the handle, which spins the stone. It is this spin that will cause the stone to move in the direction of the spin as the stone slows and the small portion of the concave underside that actually contacts the ice is affected by the pebbly ice surface.

As the stone moves down the sheet, the ice in front of it can be kept clear of debris by two of the team members (usually the "lead" and "second") who sweep the ice. Originally, brooms were used for this function. Now, specialized brushes are used.

All four members of a team curl stones. Each member has two attempts in each end. They curl in a defined order; the lead, second, third (also called the "vice," or the "mate"), and the "skip" (who is in charge of the squad and literally calls the shots). The last stone delivered (the "hammer") alternates between the two teams with each end.

The ability to accurately deliver the heavy curling stone to within inches of the intended target requires great skill and makes curling exciting to watch. Furthermore, in each end of a match, the constantly shifting strategy as different combinations and locations of stones occur add another dimension to the sport.