Dual citizenship is the practice of having two citizenships at the same time - having more than two is technically known as multiple citizenship, but is often referred to as dual citizenship for the sake of simplicity.
Many micronations today permit dual citizenship, thus allowing them to share citizens and making each one bigger than it would have been otherwise. Some include caveats that such citizens cannot hold high government positions, and almost all prevent dual citizens from being part of an intelligence agency. Several scandals and events have cast dual citizenship in a poor light, such as Thoenen's participation in Babkhan intelligence and debates over Bagelcratian influence in Lavalon.
Among the few micronations that bar dual citizenship are St.Charlie, Sandus, the Dinarchy of Antica and Ascalon. Shireroth has long since allowed its population a maximum of two other citizenships with its Tri Citizenship law, but very few of its citizens take advantage of it. Likewise, the Empire of Austenasia only allows its subjects to hold dual citizenship with New Wessex and/or the United Kingdom.
The United Sovereign Independent Democratic Empire of Satirocity banned dual citizenship for more than six months of its existance, but now allows it.