The economics issue is that the UK sends money to Brussels (the HQ of the EU), which then gets redistributed to the various other member states. The arguments of those in favor of Brexit — the Leave Campaign — sound similar to Americans who complain about national funding which goes to programs like the National Endowment for the Arts. “Why should we have to pay for that?” The Remain Campaign, on the other hand, argues that leaving the EU (and its common market, in which Britain can sell goods to all EU states under favorable terms) would wreck the British economy, and possibly the world economy.