But first the migrants must cross great distances.
The main routes are:

SMUGGLERS' PRICES BY SEA: Africa to Canary Islands: 1,000-1,500 euros North Morocco to Spain: 1,000 euros Libya to Italy: 1,500-2,000 euros BY LAND: Sub-Sahara to Morocco: 1,000-2,000 euros Through Mali: 1,000 euros Across Sahara: 1,700-3,400 euros BY AIR/LAND/SEA: South Asia to Africa to Europe: 9,000-16,000 euros Source: UN

Route: West African coast
Destination: Canary Islands
Via: Liberia, Sierra Leone, Guinea, Guinea-Bissau, Senegal, The Gambia, Mauritania and Western Sahara to northern coast of Morocco
Dangers: sea crossing to Canaries
Who: Mainly migrants from these countries

Route: Western Sahara
Destination: Canary Islands
Via: Mali, Mauritania, Western Sahara or southern Morocco
Dangers: Crossing Sahara, guerrillas
Who: Mainly migrants from Ivory Coast, Ghana, Burkina Faso, Togo and Benin

Route: Central Sahara
Destinations: Canary Islands, Spain, Italy
Via: Niger, northern Mauritania, Western Sahara or southern Morocco; northern Morocco; Tunisia or Libya
Dangers: Crossing desert and sea
Who: Mainly migrants from countries south of Niger, via Cameroon and Nigeria

Route: Eastern Sahara
Destinations: Lampedusa, Sicily, and Malta
Via: Tunisia and Libya
Dangers: Desert and sea crossing
Who: Mainly migrants from Sub-Sahara Africa

Route: Horn of Africa to Libya
Destinations: Lampedusa, Sicily, and Malta
Via: Sudan
Dangers: Desert and sea crossing
Who: Mainly from Somalia and Ethiopia

As the closest European country to the African continent, Spain is on the frontline for illegal migration. From there, migrants often make their way to other European countries.

Spain's enclaves of Ceuta and Melilla in northern Morocco are initial targets for many migrants. Once detained they can be expelled, repatriated or sent to mainland Spain, where many are reported to be released, pending expulsion.

The enclaves' authorities were forced to double the size of border fences around the coastal territories in 2005 when hundreds of migrants attempted to scale the defences. Two migrants were shot dead by a Moroccan guard.

For years, people have risked crossing the sea to get to mainland Spain, but in 2006 there was a closer focus on its islands - thousands headed for the Canary Islands in former African fishing boats, prompting an increase in joint "Frontex" patrol operations by Spain, the EU and African nations. But tightening security at one departure point simply seems to shift it elsewhere.

The latest report on migration by the Organisation for Economic Co-operation and Development (OECD) says African migration to developed countries is marginal in relation to overall flows.

The majority of African migrants living overseas are in Europe - about 4.6m compared with 890,000 in the US, according to the International Organization for Migration. But the Migration Policy Institute believes there are between seven and eight million irregular African immigrants living in the EU - the actual number changing depending on regularisation schemes in the member states.

About two-thirds of Africans in Europe are from north Africa (Algeria, Morocco and Tunisia). An increasing number are travelling from Sub-Saharan Africa, mainly heading for the former colonial powers of France, Germany, Italy and the UK.

Most Sub-Saharan migrants are from West Africa - Ghana, Nigeria and Senegal, in particular.

About 22,016 people reached Italy by boat in 2006, down slightly from 2005. But the sea crossings are not without their dangers - it is thought hundreds die attempting to reach Europe. In June this year, 24 Africans drowned after a dinghy capsized south of Malta.

Having migrated, many migrants send money home to family they have left behind. Billions of dollars each year is sent back to Africa from the diaspora around the world - in some cases making up a sizeable chunk of the home country's GDP.