Pemba known as 'Al Jazeera Al Khadra' (the green island, in Arabic) is an island forming part of the Zanzibar archipelago, lying off the east coast of Africa in the Indian Ocean. It is situated about 60 kilometres to the north of the island of Zanzibar. It lies 50 kilometres east of mainland Tanzania. Together with Mafia Island (south of Zanzibar), they form the Spice Islands. In 1988, the estimated population was 265,000, with an area of 980 km².

Unlike Zanzibar, Pemba is formed from a land mass rather than coral reefs and sand banks. Its landscape is therefore more rolling, with green hills and fertile valleys, and it has a very jagged coastline. Most of the island is dominated by small scale farming. There is large scale farming of cash crops such as cloves.

Pemba’s inhabitants partly descended from traders from the Persian Gulf region who settled on the island beginning in the 10th cent. The Portuguese occupied the island in the 16th cent. but were displaced by Omani Arabs in 1698.  Pemba was seized by the Sultan of Muscat (now Oman). He was so enchanted by the Spice Islands that he installed himself in Zanzibar and ruled Muscat from there. In 1822 the island was conquered by Sayyid Said (later the sultan of Zanzibar.

When the Western Colonial powers came to East Africa the British forced the Sultanates of Muscat and Zanzibar to separate and then administered the Spice Islands in the name of the Sultan. All the while, the Arab dhows would ply the trade winds down from the Arabian Peninsula to East Africa. With the winds they would take cloves to India, textiles back to the Arab lands and silver and wood to the Spice Islands of Unguja and Pemba. 

The dhows have remained a constant throughout the history of Pemba. To this day they ply the run from Wete to Shimoni in Kenya and, when the winds are favourable they plough through to Northern Mozambique. 

Previously, the island was visited rarely due to inaccessibility and a reputation for political violence, a center for traditional medicine and witchcraft. People would come all the way from even Zaire to seek spiritual and physical healers. There is a very large Arab community on the island who immigrated from Oman. The population here is a mix of Arab and original Swahili inhabitants of the island.

The most important towns in Pemba are Chake Chake, Mkoani, and Wete. Northern Chake Chake is located on a hill with a view on the bay where the tides determine when a dhow can enter the harbour. East of this place, on a peninsula, you can find the Ras Mkumbu that houses the oldest ruins of the island (14th century).

Pemba is very fertile and the locals grow mainly rice and red. They also grow coffee in small quatities. Pemba is also starting to get known for its dive sites, with vertiginous drop-offs, untouched coral and very abundant marine life.

Pemba is also famous for its rich fishing grounds. Between the island and the mainland there is the 20 miles wide Pemba channel, which is one of the most profitable fishing grounds for game fishing on the East African coast.

Access to the island is by air, with regular scheduled flights from both mainland Tanga or via its sister island Zanzibar. Chake Chake is the main town and home to the airport and main hospital.

Reference

http://www.answers.com/topic/pemba
http://www.tribes.co.uk/regions/islands/pemba_island
http://en.wikipedia.org/wiki/Pemba,_Tanzania
http://www.zanzibarmagic.com/english2nd/history.htm