ABSTRACT Public organisations are increasingly practising open innovation. Declining budgets, demand for greater participation and growing complexity of today’s social problems are forcing public sector employees to integrate external agencies into their organisational processes. While this eagerness to open up is well-documented, the effects of openness of public organisations on innovation outcomes are not well understood. This article addresses this crucial gap by analysing the extent of involvement of external sources in the innovation process of public sector workplaces and examining the relationship between such involvement and innovation outcomes. The findings suggest that openness and external knowledge is associated with positive organisational returns. Findings also show that public sector workplaces utilise external knowledge to generate product or service innovations, but not to generate organisational process changes.