Iraq's government is fighting a rebellion which has seen it rapidly lose control of predominantly Sunni Arab northern and western parts of the country.
The militant group Isis is widely perceived as leading the uprising, but it is not acting alone.
Here, jihadist groups analyst Aymenn Jawad Al-Tamimi looks at who is taking part in the insurgency.
ISLAMIC STATE IN IRAQ AND THE LEVANT (ISIS)
While Isis has grabbed headlines around the world, there can be a tendency to overstate its role in the insurgency.
Indeed, initial media coverage of events like the fall of Falluja and Mosul often portrayed the insurgent offensives as solely the work of Isis. The perception is fed by Isis' social media output that puts great weight on holding parades and raising the banner in assertions of power.
However, it cannot be denied that Isis is at least leading the majority of moves into new territory to wrest control from government forces. This is partly because Isis is better equipped, having seized advanced weaponry and uniforms from security forces over the past couple of years.
Furthermore, when it comes to asserting authority in a new area, one advantage Isis has over other groups is its superior financial resources, which enable it to engage in outreach to locals.
It is this outreach, combined with the group's restrained conduct in Falluja, that gives Isis an advantage in securing tribal support in Anbar in particular, where some negotiated handovers of territory to Isis' authority have taken place and where hope has been expressed that Isis will not be harsh in imposing its strict view of Islamic law on the tribes.
One of Isis' slogans is "remain and expand", which is precisely what it has done in Syria and Iraq.
In Iraq, Isis has a presence in most of the localities that have fallen into insurgent hands, spearheading the takeovers of Mosul and Tikrit.
In both cities, Isis has asserted itself as the main authority. Indeed, from the "city charter" issued by Isis for Mosul, the group has made it clear it wishes to turn Mosul into Iraq's version of the city of Raqqa, its de facto capital.
Conversely in Falluja, Isis has not issued a similar charter and has been more tolerant of practices it deems un-Islamic, illustrating that it still does not exercise full control over the city and has to share power with a military council composed of a variety of insurgent groups in the wider area, backed by tribal support.
Estimates for Isis' numerical strength in Iraq range from just 2,000-3,000 to perhaps 10,000 or more. Considering the sheer number of operations Isis has been able to carry out in comparison with other groups, the higher end estimates seem more plausible.
JAMAAT ANSAR AL-ISLAM (JAI)
JAI is a rival of Isis and is primarily based in Nineveh (particularly Mosul), Kirkuk and Salahuddin provinces, though its numerical strength is not known. While JAI shares Isis' aspirations for a caliphate, it rejects Isis' claim to represent an actual state rather than a mere group.
JAI and Isis fought one another throughout last year because of a dispute stretching back to Isis' previous incarnation as the Islamic State in Iraq (ISI).
Since the outbreak of the insurgency in Anbar province in December 2013, some fighters have taken up the JAI banner in the Falluja area, and more recently the group claimed a role in the fall of Tikrit.
Rumours have since emerged of the arrest and killing by Isis of multiple JAI members in Mosul and Tikrit. In Mosul, dozens of JAI members have pledged allegiance to Isis rather than resist.
While exact numbers are difficult to determine, the Army of the Men of the Naqshbandi Order (Jaysh Rijal al-Tariqa al-Naqshbandia, or JRTN) and its front groups likely constitute the second largest insurgent grouping in Iraq after Isis.
Led by Saddam Hussein's right-hand man, Izzat Ibrahim al-Douri, JRTN is the main front for Baathist insurgents. JRTN espouses a blend of the banned Baathist Party's ideology (pan-Arab, secular nationalism) and Naqshbandi Sufi Islam, while emphasising the language of jihad in an attempt to garner religious legitimacy.
As most Sunni Arabs are not Naqshbandis, JRTN set up front groups of Baathists, which have become unified under the "General Military Council for Iraq's Revolutionaries" (GMC).
Though co-ordination with Isis is not admitted, it is apparent that JRTN and its front groups have worked with Isis not only in Mosul but also in Tikrit and Diyala province.
Such co-operation suggests JRTN hopes for some kind of power-sharing arrangement that could eventually get the better of Isis and lead to a restoration of the Baathist state, as existed under Saddam.
In public statements, JRTN tries to avoid mentioning Isis by name and it is clear that there is no wish to engage in an all-out war against Isis, though on both sides there is profound distrust on account of ideological differences.
The JRTN's front group, the GMC, also operates in the remaining parts of Anbar still contested with government forces, such as Ramadi and Karma, and maintains a presence in Falluja.
JAYSH AL-MUJAHIDEEN (JAM)
A group dating back to the 2003 invasion, JAM aspires to overthrow the central government and is anti-Shia in outlook.
Recent evidence suggests it has forged a special relationship with JAI as a counter to Isis, which JAM deems extremist, and there have been indications of co-ordination in the Hawija area, near Kirkuk city.
JAM also places emphasis on working with local tribes, and appears to be maintaining a strong presence in Karma. However, tensions have emerged there with Isis over allegations that the jihadist group has been attempting to gain a monopoly on the movement of commodities, though there have been no reports of actual infighting yet.
ISLAMIC ARMY OF IRAQ (IAI)
Another traditional insurgent brand, the IAI is distinguished from the other groups in that after the US withdrawal at the end of 2011, IAI formally demobilised and set up an activist wing - the Sunni Popular Movement- aiming to push for a Sunni Arab federal region.
On account of joining the political process, the IAI is criticised by Jam, which denies any co-ordination.
Beginning with this year, however, the IAI has taken up the cause of armed struggle again, with evidence of the group's presence primarily emerging from Diyala and Salahuddin provinces.
One should however be wary of spokesmen's spin about having thousands of fighters under the banner. In reality, the group was much weakened through abandonment of the IAI for the Sahwa, or Awakening, forces (anti-al-Qaeda Sunni militia) and the joining of the political process.
As of now, the IAI effectively offers the choice to the central government of either giving in to the IAI's calls for a Sunni federal region or of preparing for the capture of Baghdad.
Besides the five main insurgent brands, there are groups by other names, some going back to the US-led invasion, others being more recent brands.
Examples of the former include the nationalist 1920s Revolution Brigades, whose commander in Tikrit was reportedly killed by security forces recently, and a small group in the Falluja area called Saraya al-Madina al-Munawara (The Honoured City's Brigades), which claims good relations with Isis.
However, there is too little evidence to suggest these groups play a decisive role in the fighting.
Aymenn Jawad Al-Tamimi is a Shillman-Ginsburg Fellow at the Middle East Forum who specialises in jihadist groups in Syria and Iraq. Follow him @ajaltamimi