We use comprehensive data from Denmark that merge online job advertisements with a matched employer-employee dataset and a firm-level dataset with information on revenues and value added to study the relationship between vacancy-posting and various firm outcomes. Vacancy-posting is associated with a 4.4 percentage point increase in a firm's hiring rate and 85% of the additional hiring occurs within two months. The response of hiring from employment is twice as large as the response of hiring from non-employment. Firms that are smaller, low-wage and fast-growing are associated with larger hiring responses and that response materializes faster at larger firms, low-wage firms and fast-growing firms. We also find that separations are associated with subsequent vacancy-posting and this effect is stronger for separations to employment, consistent with replacement hiring and the presence of vacancy chains. Growth in revenue and value added strongly predict vacancy-posting, with negative shocks having a stronger effect than positive shocks and larger shocks having less-than-proportional responses.