What is the role of the army?

Observers say the army has always been the key power in a highly fluid, opaque and dangerous situation - able either to shepherd Egypt towards a democratic future of free elections, or to uphold the status quo.
In contrast to the security police, it has pledged not to use violence to quell what have been near-universally peaceful protests.
This apparently neutrality has won it praise from other governments, concerned about the possibility of a bloody denouement of this crisis.
After the 10 February Supreme Military Council meeting, a military communique was issued appearing to back the protesters' demands, prompting a day of speculation of a military take-over.
It was therefore a shock to protesters when Mr Mubarak gave a state address some hours later not offering his resignation, but expressing more determination than ever to ride out the crisis.
Speculation then turned to the possibility of a split in the army, with an old guard backing the old order and younger officers more in harmony with the protesters.
The air force, whose aircraft have buzzed the protests' epicentre in Cairo's Tahrir (Liberation) Square as a show of intimidating force, was believed to have remained loyal to the president, who was himself a military pilot and commander.

What caused the street clashes early on in the conflict?

Countrywide protests after Friday prayers on 28 January were met with typically repressive measures by the security police, but the determination and sheer numbers of protesters proved overwhelming.
Government tactics appeared to be in disarray. Security police melted away, and heavy military armour appeared on the streets to the cheers of protesters.
There followed several days of carnival-like protests centred on Cairo's Tahrir (Liberation) Square, effectively celebrations of the newfound freedom and mutual respect among protesters.
It culminated in the so-called "march of the million" on 1 February.
However, a more sinister atmosphere was emerging, as state media reported a wave of looting in Cairo, causing many people to set up armed neighbourhood watch groups to protect their homes.
Government loyalists also voiced frustration, especially with the media for giving too much prominence to the protests.
On 2 February, pro-Mubarak marchers tried to gain access to Tahrir Square and what had been a peaceful scene deteriorated into vicious stone- and petrol-bomb-throwing street battles.
Barricades were erected by the anti-Mubarak side and they appeared ready to dig in for a long occupation of the square until the president resigned.

Is this the long-awaited "Arab Spring"?

The consequences of Egypt's unrest could be great for other Arab countries and rulers. Democracy is a rare commodity in the region and several other governments could be sitting on similar political volcanoes.
What surprised many Egypt-watchers was the vehemence and cohesiveness of the first day of protests, which seemed to change the entire political landscape within a few hours.
Protests were seen in the second city, Alexandria, as well as in many large conurbations in the Nile Delta, Suez and Ismailiya. It is testimony to the resilience and tenacity of Mr Mubarak's rule that he was not swept immediately away like Mr Ben Ali.
Mr Mubarak's most influential Western ally, the US, has been caught in a serious bind. Should it live up to its professed desires for democracy or support the Egyptian president for fear of loss of influence and what might follow his overthrow?
It has been able to exert little influence beyond calling for an "orderly transition" at the earliest opportunity.
Other Arab autocrats offered Mr Mubarak support, but faced mass protests of their own.
After the initial flurry of imitative protests in Yemen, Jordan, Algeria and elsewhere, their rulers made hasty concessions. Meanwhile, their simmering populations awaited the outcome of the struggle in Egypt.