Birdwatching or birding is the observation and study of birds with the naked eye or through a visual enhancement device like binoculars. Birding often involves a significant auditory component, as many bird species are more readily detected and identified by ear than by eye. Most birdwatchers pursue this activity mainly for recreational or social reasons, unlike ornithologists, who engage in the study of birds using more formal scientific methods.

The term birdwatching was first used in 1901 while bird was recorded as a verb in 1918. The term birding was also used for the practice of fowling or hunting with firearms, as in Shakespeare's The Merry Wives of Windsor (1602): "She laments sir... her husband goes this morning a-birding."The terms birding and birdwatching are today used interchangeably, although birding is preferred by many since this includes the auditory component involved in locating and identifying birds.

The term twitcher, sometimes misapplied as a synonym for birder, is reserved for those who travel long distances to see a rare bird that would then be "ticked" off on a "list". The term appeared in the 1950s, said to have originated from a phrase used to describe the nervous behaviour of Howard Medhurst, a British birdwatcher. Before that the term for those who chased rarities was pot-hunter, tally-hunter or tick-hunter. The practice of travelling long distances to see rarities was aided by the rising affordability of cars.

The goal of twitching is often to accumulate species on one's lists. Some birders engage in competition with one another to accumulate the longest species list. The act of the pursuit itself is referred to as a twitch or a chase. A rare bird that stays put long enough for people to see it is called twitchable or chaseable.

Twitching is highly developed in the United Kingdom, the Netherlands, Denmark, Ireland, Finland and Sweden. The smaller size of these countries makes it possible to quickly travel inside their borders with relative ease. The most popular twitches in the UK have drawn large crowds, such as a group of approximately 5,000 people who came to view a Golden-winged Warbler in Kent. Twitchers have developed their own vocabulary. For example, a twitcher who fails to see a rare bird has dipped out; if other twitchers do see the bird, he may feel gripped off. Suppression is the act of concealing news of a rare bird from other twitchers.