This paper examines the importance of competition in the growth and development of firms. We make use of the large-scale natural experiment of the shift from an economic system without competition to a market economy to shed light on the factors that influence innovation by firms and their subsequent growth. Using a dataset from a survey of nearly 4,000 firms in 24 transition countries, we find evidence of the importance of a minimum of rivalry in both innovation and growth: the presence of at least a few competitors is effective both directly and through improving the efficiency with which the rents from market power in product markets are utilised to undertake innovation.