Bolivia has a long tradition of organised political protests. It was the first country in South America to have a left-wing revolution in 1952, which nationalised the mines and gave universal suffrage.
By James Painter
BBC regional analyst
It has a history of strong civil society and weak government. The latest surge in protest movements began in the late 1990s, largely provoked by little improvement in the conditions of the poor, largely Indian, majority and disillusionment with the traditional political parties.
Slum dwellers of El Alto
They have been the biggest protest group in recent weeks.
Based in the huge township of El Alto, on the altiplano (highland plain) above La Paz, they have frequently blockaded one of main roads into the city.
Indians from El Alto have been flocking to protests in La Paz
El Alto has a fast-growing population of 750,000, most of whom are recently-arrived Aymara rural migrants.
Neighbourhood committees, with a strong sense of community support, are the key organising force.
Their leader is Abel Mamani.
They were instrumental in bringing down the government of Gonzalo Sanchez de Lozada in October 2003, and in opposing the provision of water supplies by a French-owned company.
They are in favour of nationalisation of the oil and gas sector, an end to free-market economics and more political rights for indigenous people.
Evo Morales and the coca farmers of the Chapare
Evo Morales is an Aymara Indian who came to prominence as a leader of the coca-growers' union in the region of Chapare in central Bolivia, where most of the country's coca (the raw material for cocaine) is grown.
His party, the MAS (Movement towards Socialism), came second in the 2002 general elections.
He is vehemently opposed to US intervention in the country, particularly around the issue of coca eradication.
Mr Morales does have ties with President Hugo Chavez of Venezuela, which is another reason he is strongly disliked by Washington.
Evo Morales is one of the leaders of the coca growers' union
He is normally considered less radical and more flexible than other Indian leaders. However, he has recently stressed he is now in favour of the nationalisation of gas and oil reserves, which he considers "not negotiable'".
He is also in favour of new elections.
Felipe Quispe and peasant farmers
Felipe Quispe is a radical Aymara peasant leader from the highlands.
He believes in the formation of an independent Aymara state, and constantly attacks Bolivia's "white" elite.
He sprung to fame in 1998 when he became head of the powerful peasant federation, the CSUTCB.
He and his party, the MIP (Pachakuti Indigenous Movement), won six seats in Congress in the 2002 elections, but he later resigned to return to grass-root activism.
His radical rhetoric does attract support amongst highland Aymaras keen to assert indigenous and land rights, but he is not considered a key figure in the current protests.
He is also known as "El Mallku", "condor" or leader in Aymara.
Historically, the Bolivian miners were probably the most militant trade union group in the whole of Latin America, who formed the backbone of the powerful workers' confederation, the COB.
But their numbers were seriously reduced in the mid-1980s after the world price of tin crashed and around 25,000 were thrown out of work.
Many of them turned to other activities, such as coca-growing, or stuck to working precarious mines as members of cooperatives.
Miners have been very active in recent social struggles
They have been very active in recent struggles to resist the privatisation of pensions.
In the current protests, they are the ones maintaining an old Bolivian protest tradition of letting off very loud explosions of dynamite.
Protesters in Cochabamba
Cochabamba is Bolivia's fourth city (after La Paz, Santa Cruz and El Alto).
Protesters there sprung to international prominence in early 2000 when a series of violent clashes eventually led to the government retracting the selling-off of water provision to a subsidiary of the US multinational, Bechtel.
Urban users, rural farmers and coca growers from nearby Chapare united in mass protest, which was one of the first successful attempts to oppose the free-market model of the last 20 years.
The leader of the Cochabamba marches was Oscar Olivera, who is now one of the leaders of the movement to nationalise Bolivia's gas. The main roads into Cochabamba have been cut off by protesters demanding the nationalisation of resources and a new Constituent Assembly.
Indigenous and peasant groups in Santa Cruz
Indians in the eastern lowland department of Santa Cruz are a mixture of immigrant communities from other parts of the country and indigenous groups such as the Guaraní, Ayoreo, Chiquitano and Guarayos.
They have become involved in land disputes as the pressure on the land increases with the expansion of soya, timber and cattle ranching.
The main organisation representing Indians is CIDOB, but some are also members of the more radical MST (Landless Peasant Movement), not dissimilar to the movement of the same name in Brazil, which has been involved in land seizures over the last 10 years.
Most notable was the occupation of three BP-owned oil installations in August 2004.
In the current disputes, Guaraní Indians have taken over oil fields run by Repsol and BP, forcing them to halt production.
The Santa Cruz elite
Historically, many crucenos have liked to distinguish themselves as "cambas" in contrast to the "collos" of the highlands.
Their demands for more regional autonomy have become more strident in recent months, in part due to the strength of the highland-based protest movement and the possibility of nationalisation of the gas sector.
They argue that as the most dynamic and fastest-growing sector of the Bolivian economy where much of the country's gas is based, they should keep a large share of the gas revenues.
Business organisations, such as cattle farmers and agribusiness sectors, are strong supporters of the Pro Santa Cruz Committee.
Large demonstrations in January this year pressed their claims for greater autonomy.
Local leaders say they will go ahead with their own referendum on autonomy in August this year, with or without the approval of the national government.