The implementation of Industry 4.0 (I4) technologies has gained momentum due to several inherent benefits associated with their adoption. However, the benefits of I4 technologies are yet to be realised to the full potential, specifically in the case of emerging economies. Managers need to focus on certain critical factors for the successful implementation of I4 technologies. Though some studies have proposed factors for implementing I4 technologies, empirical examination of critical factors still lacks in the published literature. This study proposes and empirically analyses the critical factors for adopting I4 technologies in the following Indian manufacturing industries: electrical/electronics, automotive, textiles, paper and plastics. The key factors across six different categories (organisational, workforce management, external support, technological infrastructure, usage of data and regulations) are examined. Further, the contingency effects of firm size and industry sector are also examined. The results are useful for managers in manufacturing industries as it can help them to understand the key factors for adopting I4 technologies. The results are equally useful for managers who are planning to implement I4 technologies in their firms or are in the early phase of I4 implementation.