This paper examines innovation among very small firms and provides new insights into both internal and external determinants of patenting. Applying a non-linear panel data approach to about 160,000 observations on manufacturing firms in Sweden for the period 2000-2006, the following facts emerge: (i) in contrast to larger firms, innovation in micro firms with 1-10 employees is not sensitive to variation in internal financial resources, (ii) skilled labour is even more important for innovation among micro firms compared to other firms, (iii) affiliation to a domestically owned multinational enterprise group increases the innovation capacity of small businesses, (iv) small firms' innovation is closely linked to participation in international trade and exports to the G7-countries, and (v) there is no statistically significant evidence that proximity to metropolitan areas, or presence in a specialized cluster, increases the innovativeness of the smallest firm