PurposeSeveral empirical studies indicate that the existence of a large informal sector is a major obstacle to firms’ choices of innovation strategies. This paper aims to address this issue and investigates the effect of the informal sector on the innovation of formal firms in Greece.Design/methodology/approachUsing the World Bank’s Enterprise Survey data, the impact of informal competition on formal firms’ innovation in Greece is investigated by testing whether formal firms use innovation as a tool to protect and sustain their competitive advantage vis-à-vis informal firms and whether overall and informal competition has an inverted-U relationship with the innovation of formal firms. The effects of bribing and other variables drawn from the empirical literature are also controlled for.FindingsThe findings fill a gap in the literature regarding the effects of the informal sector on formal economic activity in Greece, by indicating that the informal sector puts pressure on formal firms to innovate, in order to differentiate their product or service and enhance their productivity and by offering learnings to help policymakers to promote innovation in Greece.Originality/valueThe originality of this study is that it investigates the impact of informal competition on formal firms’ innovation in Greece, a developed economy with a large informal sector. It does so by focusing on the effects that formal firms’ informal practices have on their competitors’ innovation activities, and the role of informal competition in creating and sustaining a competitive advantage in Greece.