A handshake is a short ritual in which two people grasp one of each other's like hands, in most cases accompanied by a brief up and down movement of the grasped hands. When making a bet and confirming the bet with a handshake, it is usually held that the instant the two hands touch willingly, the bet becomes official. Using the right hand is generally considered proper etiquette. There are various customs surrounding handshakes, both generically and specific to certain cultures. Different cultures may be more or less likely to shake hands, or there may be different customs about how or when to shake hands. Handshakes are known to spread germs. 
The first documented handshake in human history appears on the monument of Kalhu, showing the Assyrian king Shalmaneser III and Marduk-zakir-šumi I of Babylon shaking hands in a public display of Assyro-Babylonian friendship.  Archaeological ruins and ancient texts show that handshaking was practiced in ancient Greece as far back as the 5th century BC; a depiction of two soldiers shaking hands can be found on part of a 5th-century BC funerary stele on display in the Pergamon Museum, Berlin (stele SK1708) and other funerary steles like the one of the 4th century BC which depicts Thraseas and his wife Euandria handshaking (see images on the right). The handshake is thought by some to have originated as a gesture of peace by demonstrating that the hand holds no weapon.
There are various customs surrounding handshakes, both generically and specific to certain cultures:
The handshake is commonly done upon meeting, greeting, parting, offering congratulations, expressing gratitude, or completing an agreement. In sports or other competitive activities, it is also done as a sign of good sportsmanship. Its purpose is to convey trust, respect, balance, and equality. If it is done to form an agreement, the agreement is not official until the hands are parted 
- In Anglophone countries, in business situations. In casual non-business situations, men are more likely to shake hands than women.
- In Switzerland, it may be expected to shake the women's hands first.
- Austrians shake hands when meeting, often including with children.
- In Russia, a handshake is rarely performed by opposite sexes. Men shaking hands with women can be considered impolite, since hand-kissing is preferred as a ritual for greeting a lady. However, kissing the hand is considered unsuitable for business situations.
- In some countries such as Turkey or the Arabic-speaking Middle East, handshakes are not as firm as in North America and Europe. Consequently, a grip which is too firm will be considered as rude. Hand shaking between men and women is not encouraged in countries where the majority religion is Islam.
- Moroccans also give one kiss on each cheek (to corresponding genders) together with the handshake. Also, in some countries, a variation exists where instead of kisses, after the handshake the palm is placed on the heart.
- In China, where a weak handshake is also preferred, people shaking hands will often hold on to each other's hands for an extended period after the initial handshake.
- In Japan, it is appropriate to let the Japanese initiate the handshake, and a weak handshake is preferred.
- In India and several nearby countries, the respectful Namaste gesture, sometimes combined with a slight bow, is used in place of handshakes.
- In Norway, where a firm handshake is preferred, people will most often shake hands when agreeing on deals, both in private and business relations.
- In South Korea, a senior person will initiate a handshake, where it is preferred to be weak. It is a sign of respect to grasp the right arm with the left hand when shaking hands. It is also considered rude or disrespectful to have your free hand in your pocket while shaking hands.
- Related to a handshake but more casual, some people prefer a fist bump. Typically the fist bump is done with a clenched hand. Only the knuckles of the hand are typically touched to the knuckles of the other persons hand. Like a handshake the fist bump may be used to acknowledge a relationship with another person. However, unlike the formality of a handshake, the fist bump is typically not used to seal a business deal or in formal business settings.
- The hand hug is a type of handshake popular with politicians, as it can present them as being warm, friendly, trustworthy and honest. This type of handshake involves covering the clenched hands with the remaining free hand, creating a sort of "cocoon."
- Scouts will shake hands with their left hand as a gesture of trust. This originated when the founder of the movement, Lord Baden-Powell of Gillwell then a British cavalry officer, met an African tribesman.
- In some areas of Africa, handshakes are continually held to show that the conversation is between the two talking. If they are not shaking hands, others are permitted to enter the conversation.
Handshakes are known to spread countless germs. Certain diseases such as scabies spread the most through direct skin-to-skin contact. A medical study has found that fist bumps and high fives spread less germs than handshakes.
In light of the 2009 H1N1 pandemic, the dean of medicine at the University of Calgary, Tomas Feasby, suggested that the fist bump may be a "nice replacement of the handshake" in an effort to prevent transmission of the virus.
Atlantic City, New Jersey Mayor Joseph Lazarow was recognized by the Guinness Book of World Records for a July 1977 publicity stunt, in which the mayor shook more than 11,000 hands in a single day, breaking the record previously held by President Theodore Roosevelt, who had set the record with 8,510 handshakes at a White House reception on 1 January 1907.
On Memorial Day 2008, two friends from Muscatine, Iowa, Kevin Whittaker and Cory Jens set the Guinness World Record for the world's longest handshake at 9 hours and 30 minutes in San Francisco, CA. On 21 September 2009, Jack Tsonis and Lindsay Morrison broke the Guinness World Record for the world's longest handshake, shaking hands for 12 hours, 34 minutes and 56 seconds. This record was broken less than a month later in Claremont, California, when John-Clark Levin and George Posner shook hands for 15 hours, 15 minutes, and 15 seconds. The next month, on 21 November, Matthew Rosen and Joe Ackerman surpassed this feat, with a new world record time of 15 hours, 30 minutes and 45 seconds., certified in the latest edition of the Guinness Book of Records on page 111. At 8pm EST on Friday 14 January 2011 the latest attempt at the longest hand-shake commenced in New York Times Square and the existing record was smashed  by semi-professional world record-breaker Alastair Galpin and Don Purdon from New Zealand and Nepalese brothers Rohit and Santosh Timilsina who agreed to share the new record after 33 hours and 3 minutes.
- Dap greeting
- Fist bump
- Golden handshake
- Greeting habits
- Handshake Man
- Handshaking lemma
- Holding hands
- Scout handshake
- Fist bump can pound out flu transmission
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- Media related to Handshake at Wikimedia Commons
- The dictionary definition of handshake at Wiktionary