Summary About 90% of people are right-handed and 10% are left- handed. Handedness is associated with functional lateraliza- tion for cerebral dominance, and may also be associated with various types of psychopathology. Broadly speaking, the vast majority of humans seem to have been right-handed since the emergence of the genus Homo, some three to four million years ago. Likewise, in all societies studied, there is a large excess of right-handers. However, there have been few studies exploring the detailed history and geography of handedness, not least because adequate pre-twentieth century historical data are difficult to find, and very large sample sizes with consistent measurement methods are required for geograph- icalstudies.Thischapteroverviewsthevarioussetsofdatathat provide insight in handedness's history and geography. It is probable that about 8% to 10% of the population has probably been left-handed for at least the past 200000 years or so. Detailed data only began to become available for those born in the nineteenth century, and there is growing evidence that the rate of left-handedness fell precipitously during the Victorian period, reaching a nadirof about 3% in about 1895 or so, and then rising quite quickly until an asymptote is reached for those born after about 1945 to 1950, with 11% to 12% of men and 9% to 10% of women typically being left-handed in Western countries. Thesex ratioseems toremainconstant, not only during historical changes but also with geographical dif- ferences, and is presumably the result of a biological rather than a cultural process. Geographical differences in handedness are clearly appa- rent both between continents (as in Singh & Bryden's, 1994, comparison of Canada and India) and within continents: rates in Europe seeming to be highest in Britain, Holland, and Belgium, and falling away towards the east and south, and within countries, seen well in Stier's (1911) 1909 study of the German Army, in Leask and Beaton's (2007) study of the United Kingdom, and between the various states of the USA, in the very large Gilbert and Wysocki (1992) database. Ethnic differences in handedness are related to geographi- cal differences, with left-handedness generally being more common in White, Asian and Hispanic populations - a differ- ence seen both in the UK, and historically in the United States, wherethedifferencebetween ethnic groupshas grown smaller during the twentieth century, but was still present even for those born in the 1970s. Migration studies in the UK show that the lower rate of left-handedness in those from the Indian sub-continent is similar in those born in the UK and those born outside the UK, implying that genes rather than environ- ment are the primary source of the difference. Different rates of left-handedness can reflect either environ- mental or genetic differences between societies, and rates alone cannot distinguish the two processes. However, a math- ematical model shows that effects of different social pressure or gene frequencies can be distinguished if family data on handedness is available. That model suggests not only that geographicaldifferencesbut alsohistorical differences primar- ily reflect changes in gene frequency rather than direct social pressure.