This report assesses the impact of digitalisation on competition by examining the evolution of mark-ups and multifactor productivity (MFP) across firms of different sizes. It finds that size is positively related to mark-ups and that this relationship has strengthened over time. This trend has been accompanied by an increase in the relative productivity advantage of larger firms and both changes are more pronounced in digital-intensive sectors, suggesting that digitalisation may be an underlying driver. Policy makers may need to consider appropriate responses if digital technologies affect larger and smaller firms in a heterogeneous manner.