Using a sample of approximately 2 million job advertisements published online, this paper assesses which educational, skills and other requirements US employers demand the most. The analysis is focused on the 30 most-frequently advertised occupations in the United States, of different levels of complexity, and finds that employers are quite demanding in their job advertisements, even when these concern low- or medium-skilled occupations. Although vacancies for more complex occupations are generally more demanding than those for less complex ones, there is a lot of variation across the 30 occupations. Formal education is the most important criterion for employers in the United States; it is required in 67% of the vacancies examined. Specialised training and licenses, in contrast, appear to be less important. Of the cognitive and non-cognitive skills, service skills in particular are high in demand (called for in 49% of the vacancies). Other non-cognitive skills, both of a social and personal nature, are frequently included as well. Experience is the third key criterion that employers use to screen job applicants, appearing in 38% of the vacancies.