Is the US winning its "war on terror"? As it enters into its fifth year, trying to measure success, failure or even just progress remains stubbornly difficult. And the record for 2005 provides few easy answers.
The US administration used to talk about how it had killed or captured two-thirds of al-Qaeda's pre-9/11 leaders.
But that statistic looks increasingly irrelevant when al-Qaeda has itself evolved and mutated, with a new generation of militants and leaders over the past few years - as well as the problem that the best known al-Qaeda leaders remain at large.
President Bush has been on TV defending the US role in Iraq
The battle is now increasingly being recognised as an ideological one rather than a manhunt.
But if that is true, how do you measure recruitment, radicalisation and the broader factors which might help judge the state of play in the ideological struggle?
Some of the brutal tactics from al-Qaeda-related groups in Iraq, as well as the body count of innocent Muslims in attacks in places like Amman, may have dented some of the appeal of al-Qaeda's ideology to moderate Muslims.
However, reports of US abuses of detainees in Iraq and elsewhere have done the US no favours in trying to win people to its cause.
The furore over the alleged "rendition" and torture of suspects that has arisen in Europe at the end of 2005 also risks undermining the kind of international co-operation that is vital in defeating terrorism and fracturing crucial alliances.
European governments are also looking inwards at their own problems in trying to work out how to increase security whilst not alienating their own Muslim communities, who are often angry over what is happening in Iraq.
Different strategies between Europe and the US are becoming increasingly evident, although it is not clear which strategies are more effective. Differences in approach are growing even between the closest of allies.
Zarqawi's rise highlights how central Iraq is to the "war on terror"
Parts of the UK government are thought to be quite uncomfortable with some aspects of US counter-terrorist strategy, including the widespread use of mass detention as a policy in Iraq, as well as the use of so-called "extraordinary rendition" in individual cases which the UK has tried to keep at arms length from.
From al-Qaeda's side, Osama Bin Laden has not been heard from since a broadcast on the eve of the US elections in November 2004, and in the eyes of many observers, the past year has seen him eclipsed by the rise of Abu Musab al-Zarqawi.
Although Zarqawi officially put himself under al-Qaeda's banner, his precise relationship with the al-Qaeda leadership is the subject of considerable debate, with many analysts believing that relations are as much competitive as they are co-operative.
Zarqawi's rise to prominence is an indication of just how central Iraq has become to the war on terror. It may not have been before the war, but it is certainly now the central front.
Jordan's king called for a war on extremists after Amman attacks
It is also a "black hole" in the words of French anti-terrorism Judge Jean-Louis Bruguiere, drawing in jihadists from around the world to fight, including increasing numbers from Europe - December saw the first female European Muslim convert take part in a suicide attack.
The question will be: what happens next? How many of these people will take the skills, militancy and networks of relationships they have developed in Iraq back to their home countries?
Will Iraq thereby play the same role that Afghanistan did in the 1980s as the breeding ground for a new generation of militants? Iraq's neighbours are likely to be the first to see any signs of this, and Saudi Arabia will be especially closely watched for signs of Iraq returnees causing trouble.
Al-Qaeda may have evolved, but the ability of the core leadership to plan and direct attacks remains a fundamental unanswered question.
The London bombings on 7 July killed 52 people
The investigation continues into London's 7 July bombings, with the trail still leading into Pakistan.
Here it is suspected - but not yet confirmed - that evidence will be found to show that there was some form of international direction or support for the attacks.
But whether such attacks are planned directly by al-Qaeda's leadership or not, 2005 has shown that the danger from terrorism remains global, with serious attacks across a wide geographical spread from London to Amman to Bali.
Next year is unlikely to be any different.