Digital technologies are transforming the environment in which firms compete online. While this change has delivered wide-reaching benefits for consumers, it has also given rise to potential competition concerns. One such area of concern relates to conglomerate mergers, which occur between firms that are neither product market competitors nor in a supply relationship. This Going Digital Toolkit note describes how merger control, and in particular the review of conglomerate mergers, can be an effective tool for making online markets more competitive.