A key issue for policy makers and regulators across the OECD area is the market structures that will best deliver efficient and inclusive mobile communication services. This has led to two issues addressed in this report, namely: the recent experience in selected countries, which have changed or held constant the number of facilities based operators; and the initial experience and key questions that have arisen with wireless network sharing. These questions are related because they converge around the issue of how many facilities-based networks are optimal in providing competitive services in the same geographical location. In all OECD countries there are at least three mobile network operators (MNOs), which broadly compete on a national basis, with some countries having four or five facilities-based networks operating nationally or in the same region. Historically, the coverage and capabilities of these networks have been important factors used by operators to differentiate their offers and attract customers. Nonetheless, sharing the expense of network facilities between multiple MNOs can significantly reduce costs, especially at a time when there are demands on operators to roll out new networks or extend coverage.