President: Ali Mohamed Shein
Ali Mohamed Shein from the governing CCM (Chama Cha Mapinduzi) party was voted in as president in elections in November 2010.
He narrowly beat Seif Sharif Hamad of the opposition Civic United Front.
Under a power-sharing deal, Mr Sharif serves as one of Mr Shein's vice-presidents.
The power-sharing deal was enshrined in a constitutional amendment adopted earlier in the year to end perennial election violence.
Born in 1948, Dr Shein holds a PhD in clinical biochemistry and metabolic medicine.
He was appointed as vice-president of mainland Tanzania in 2001 and won the position in the 2005 elections.
Zanzibar has its own cabinet, known as the Revolutionary Council, and a 50-seat house of representatives. Elections, by popular vote, are held every five years.
Under the previous winner-takes-all electoral system, the opposition had no representation in government. But voters in a July 2010 referendum approved constitutional changes providing for power-sharing between rival parties.