The Wammy's House

 Wammy's House (located in Winchester, England) is one of many orphanages established by Quillsh Wammy (aka Watari). Founded after World War II, Wammy's House began as a training facility for children with exceptional intelligence and skills. After the success of the detective L, the motive of the school was to raise children to be the successor to the original L. None of the children refer to (or know) each other by their real names, instead using aliases. In addition to these protective aliases, notable individuals who graduate from Wammy's House may be assigned a 'letter' by Watari, now by his successor, Roger Ruvie. Until the holder of that letter dies, they are understood to be recognized by the current L and as all that have connections to Wammy's House as having significant potential to positively affect the world, and work for its change. The letters closest to L (M and N) are often direct candidates for L's succession...

Information
The orphanage is first introduced in chapter 59 (shown briefly in the anime equivalent episode 26), when Roger Ruvie, a friend of Watari's and current head of Wammy's House, learned of his passing. At the end of the chapter, he also learns that L is dead, and informs the two top students of the orphanage, Mello and Near. After learning of L's death and refusing to work with Near, (but Near is nonchalant about the idea) Mello leaves the orphanage, heading off to America. Near and Matt later depart from the orphanage at some point during the five-year time skip, with Near eventually setting up the SPK, while Matt's whereabouts remain unknown in canon.

When Light Yagami learns of Wammy's House, he sends Aizawa and Matsuda to investigate. As both L and Watari are dead, Roger tells the two detectives what he knows, including information on the two top successors. However, as even Roger did not know of their real names, and there were no photos left of them, the only evidence of their identities that the investigation team and Light had to go on were two portraits, drawn by a former student of the House named Linda, who had since become a professional artist. When Near and Mello finally meet again, Near gives Mello his only photo back and tells him that he has made sure that anyone who knew him at Wammy's would not divulge information about him.

Later in the series, Matt, having been contacted by Mello, joins up with Mello in the race to catch Kira. However, they both die shortly before the finale, consequences of their plan to kidnap Kiyomi Takada. In the epilogue, Near is shown to have become the new L, with Roger in the role of Watari.

In the post-series one-shot, Near reveals that none of the children in the House ever saw L's face or directly spoke to him, only having heard him once through a monitor broadcast when he revealed his true reasoning behind being a detective. L favored Mello and Near as candidates, due to their refusal to question him and a "nasty look" in their eyes.

In Another Note
In the novel Death Note: Another Note - The Los Angeles BB Murder Case, Mello's recollection of Wammy's House is somewhat different, as he attests to having known and met L, who told him of three cases he had worked on (The BB Case being one). The novel gives more insight into Wammy's House, characterizing it as more of an institution that caused would-be successors to feel pressure to succeed L. The first child in line to be L's successor, A, eventually committed suicide due to this pressure, while B (the next successor in line) ran away and later became a serial killer (commonly known as "BB" or Beyond Birthday).

A and B are respectively referred to as being from the "first generation" of L, while Mello and Near are described as being from the "fourth generation". Three other Wammy's students (X, Y and Z) are briefly alluded to as being the last students of the first generation, though no further information on them is given.

In L: Change the WorLd
At the end of L: Change the WorLd, L, with only two days left to live, brings the "Boy" to Wammy's House. He names the "Boy" as "Near" and then leaves him in the care of the orphanage. Note that in the movie version, it is not the same Near as in the manga and anime.

Characters related to Wammy's House
Indicates that the character does not have a Letter. (-)

Indicates that the character is now deceased. ( † )

X, Y, and Z - Only briefly alluded to at the end of Another Note, they are referred to by Mello as three children that appeared in the "Detective Wars" bio-terror case with L.

Various other children are depicted in both chapter 59 and the one-shot special's flashback, though none are given any names.

Film characters

 * K - A former student of Wammy's in L: Change the WorLd, who has become part of a bioterrorist organization which plans to "cleanse" the world of its excess population by a deadly virus.
 * F - A former Wammy's student and colleague of L's that dies early on in L: Change The WorLd, while on a deadly rescue mission in Thailand.
 * D, P, Q, G, I, E - Shown on L's mailing list in L: Change the WorLd.
 * R, V, T - Also shown on L's mailing list however their letters are grayed-out along with B's, implying they were killed.

Near's Wammy House Flashback
Wammy House is recalled by Near in a flashback in Death Note Relight 2: L's Successors, and in that flashback some characters are shown in their younger years, or they look exactly the same (like Near). There are also other children that appear in flashback that are not named. They present what children normally like to do in Wammy's House.

Trivia

 * Wammy's_House_in_manga_and_anime.jpg large cross is present on the roof of the orphanage in the manga, however the cross does not appear in the anime.
 * Near's Wammy's House flashback is shown twice: in the main series and in the post-series one-shot.