Abstract: This chapter examines the use of family ties in the application of antitrust law. Competition authorities in Argentina, Brazil, Indonesia, and Turkey have relied on family ties in the contexts of merger control and scrutiny of anticompetitive agreements. Authorities have converged in using family ties to define the boundaries of an enterprise in merger review. However, there is divergence in the use of family links either as evidence of bid rigging or, conversely, as a single entity defense to bid rigging. The greater relevance of family ties in antitrust enforcement in developing countries points to an unnoticed source of variation in comparative antitrust law, and shows the adaptability of their competition laws to local circumstances. Similarly to the treatment of legal persons linked by equity ties, antitrust law’s “veil peeking” – or disregard of legal separateness – of natural persons linked by family ties does not necessarily require a showing of fraud or abuse.