This paper presents results from econometric studies on the determinants of various forms of international activities of firms. The data were collected in 1994/95 in 849 manufacturing firms in Lower Saxony, a German federal state, as part of the Hannover Firm Panel project. Important results from this first empirical study on exports, foreign direct investments, and international licensing using a large rich set of micro data on German firms are: (1) The export/sales ratio is higher in larger, more human capital intensive, and more technology intensive firms. (2) The probability that a firm has a production plant in a foreign country that produces goods similar to those produced in Germany (i.e. is a horizontally integrated multinational enterprise) is higher for firms that introduced new products, are large, and have experience in foreign markets due to exporting. (3) The probability that an establishment has given a license to a firm in a foreign country is higher if the establishment is large, performs research and development activities, owns patents, and is a horizontally integrated multinational enterprise. These results support theoretical considerations on the role of firm size, technology, and human capital for exports, foreign direct investments, and licensing.