The ECB has tinkered with its domestic T20 tournament several times since it first hosted one, in 2003. The latest version, the NatWest T20 Blast, has the 18 county sides divided into two groups.
Each team plays six of the teams in their group twice and the other two once. The top four teams in each group enter the knockouts. Each team is allowed to field two international players in their XI. The ECB plans to launch a new city-based T20 tournament in 2020.