Sharing economy is an emerging phenomenon without a consolidated economic approach. We focus on main economic characteristics of sharing economy, as a category of peer-to-peer markets, which include collaborative consumption and redistribution markets. Peer-to-peer markets create a positive externality when exploiting idling capacity, adding further exchange advantages to those usually related to classical two-sided markets. Sharing economy differs from peer-to-peer redistribution markets, where a transfer of full ownership of goods occurs, because goods are used to provide services excludable but non-rivalrous. Problems arising from sharing economy growth are briefly analysed.