In this paper we investigate the factors that lead firms to cooperate withpartners from foreign countries on innovation activities. Portuguese and Germandata from the harmonised Community Innovation Survey (CIS III) allow us tocompare innovation cooperation behaviour of private firms in the two countries.Using a bivariate probit model, we show that the characteristics of firmscooperating with foreigners in both countries are quite similar. Internationalactivities other than cooperation, firm size and the importance of protectionmethods for knowledge have a positive influence in both countries on thedecision to cooperate with foreign partners. Some differences remain, however:In Germany, exporters are more likely to cooperate with foreign partners thannon-exporters, whereas in Portugal this is not the case.