Data sources for this 18-month global study included Jewish communal institutions, human rights organizations, law enforcement agencies, university-based research centers, defectors, and confidential sources. Reasonable estimates on the numbers of Skinheads in each country were obtained by tallying Skinhead numbers at rallies, marches, concerts, festivals, soccer matches, and other gatherings. The Skinhead movement is active in 33 countries on six continents. It numbers some 70,000 youths worldwide, of whom half are hardcore activists and the rest supporters. The countries where Skinheads are found in the greatest numbers are Germany (5,000), Hungary and the Czech Republic (more than 4,000 each), the United States (3,500), Poland (2,000), the United Kingdom and Brazil (1,500 each), Italy (1,000 to 1,500), and Sweden (more than 1,000). France, Spain, Canada, and the Netherlands each have at least 500 Skinheads. The Skinhead movements in these various countries are extensively linked with each other. This "Skinhead International" is maintained through the travels abroad of popular Skinhead rock bands and their fans; the worldwide marketing of Skinhead paraphernalia and recordings; the sale and trading of publications; the exchange of propaganda; and the use of electronic communications. In all the countries where they exist Skinheads engage in violence and criminal assaults on racial minorities, immigrants, homosexuals, and Jews. Separate sections of the book are devoted to each of the 33 countries.