Ambidexterity is the ability to use both the right and left hand equally well. When referring to objects, the term indicates that the object is equally suitable for right-handed and left-handed people. When referring to humans, it indicates that a person has no marked preference for the use of the right or left hand.

Only about one percent of people are naturally ambidextrous, which equates to about 80,000,000 people in the world today. In modern times, it is common to find some people considered ambidextrous who were originally left-handed and who learned to be ambidextrous, either by choice or as a result of training in schools or in jobs where right-handedness is often emphasized or required.^{[citation needed]} Since many everyday devices such as can openers and scissors are asymmetrical and designed for right-handed people, many left-handers learn to use them right-handedly due to the rarity or lack of left-handed models. Thus, left-handed people are more likely to develop motor skills in their non-dominant hand than right-handed people.

The word "ambidextrous" is derived from the Latin roots ambi-, meaning "both", and dexter, meaning "right" or "favorable". Thus, ambidextrous is literally "both right" or "both favorable". The term ambidexter in English was originally used in a legal sense of jurors who accepted bribes from both parties for their verdict.

Some people can write with both hands. Famous examples include Albert Einstein, Benjamin Franklin, Nikola Tesla, James A. Garfield, Leonardo da Vinci and footballer Ousmane Dembele.

In India's Singrauli district there is a unique ambidextrous school named Veena Vadini School in Budhela village, where students are taught to write simultaneously with both hands.

Ambidexterity is advantageous in the sport of baseball, most commonly seen in hitters. A "switch hitter" is highly prized because a batter is more likely to hit the ball successfully if they bat with the opposite hand to the pitcher's throwing hand. An ambidextrous hitter can gain this advantage, against both right and left-handed pitchers. Pete Rose, the record holder for most hits in Major League Baseball, was a switch hitter.

Switch pitchers are comparatively rare in contrast to switch hitters. Tony Mullane won 284 games in the 19th century. Elton Chamberlain and Larry Corcoran were also notable ambidextrous pitchers. In the 20th century, Greg A. Harris was the only major league pitcher to pitch with both his left and his right arm. A natural right-hander, by 1986 he could throw well enough with his left hand that he felt capable of pitching with either hand in a game. Harris was not allowed to throw left-handed in a regular-season game until September 1995 in the penultimate game of his career. Against the Cincinnati Reds in the ninth inning, Harris (then a member of the Montreal Expos) retired Reggie Sanders pitching right-handed, then switched to his left hand for the next two hitters, Hal Morris and Ed Taubensee, who both batted left-handed. Harris walked Morris but got Taubensee to ground out. He then went back to his right hand to retire Bret Boone to end the inning.

In the 21st century there is only one major league pitcher, Pat Venditte of the Seattle Mariners, who regularly pitched with both arms. Venditte became the 21st century's first switch pitcher in the major leagues with his debut on June 5, 2015, against the Boston Red Sox, pitching two innings, allowing only one hit and recording five outs right-handed and one out left-handed. During his career, an eponymous "Venditte Rule" was created restricting the ability of a pitcher to change arms in the middle of an at-bat.