The Order of the Phoenix

Summary
The Order of the Phoenix is the group that rose to counter the Knights of Walpurgis.

After the First War with Voldemort, the Order was quiescent. It became active again during Harry's school years and was picking up members following Voldemort's reincorporation after the TriWizard Tournament. During the Second War, it operated alongside the Ministry as a functioning arm of the government and the military.

Structure
The Order was loosely organized under Albus Dumbledore, and, after his death, under a council of several individuals. Members were generally formed into squads or task groups based on need, although long-term groupings were normal during the war.

Members are referred to as "Volunteer" if a title is needed, but generally by name.

History
[still in progress]

The Order Oath
"I, _____, do solemnly swear to be true to the Order of the Phoenix and its members, and to serve honestly and faithfully against all its enemies whatsoever; and to observe and obey those rules of the Order of the Phoenix established by the founders, and the orders of the officers set over me by them."

This oath is magically binding, although it's never been clear what the consequences of breaking it are.

Members of the Order
The Order included members from the First War, the early stages of the Second War, and some former members of Dumbledore's Army.

Members of the Council

 * Remus Lupin - from Dumbledore's death until his own death
 * Alastor Moody - from Dumbledore's death until his own death early in the war
 * Minerva McGonagall - from Dumbledore's death until the end of the war
 * Kingsley Shacklebolt - from Dumbledore's death until the end of the war
 * Arthur Weasley - from Dumbledore's death until his own death
 * Molly Weasley - from Dumbledore's death until her own death

Other important members

 * Neville Longbottom
 * Nymphadora Tonks