essay: Thoughts About Wands by Amy Z.
Most human magic is done using a wand. It is possible to cast spells without using a wand, but for most wizards results are unfocused (CR). House-elves and goblins are not permitted to carry wands, which is a matter of some resentment, at least for the latter (GF9, DH24).
Wands are created from wood with some magical substance at its heart. Wands are classified by means of four characteristics: length, type of wood, quality of motion when waved, and type of magical ingredient. In Britain, the most well-known wandmaker is Mr. Ollivander (PS5, GF18). His shop, Ollivander's (Makers of Fine Wands since 382 B.C.) is located in Diagon Alley. Another European wandmaker is Gregorovitch (GF18). When a wand is damaged or broken, its effects can be unpredictable, even if patched together with Spellotape (CS, esp. CS16).
Although there is no specific rule about which kind of wood a person's wand should be, some wands are particularly well suited to their owners. Notes about specific wands are given below.
some famous wands and their characteristics
pleasantly springy, 12 1/4", single hair from the tail of a particularly
fine male unicorn
See note below on Cedric's wand core. Cedric, who is friendly and unassuming, carries a wand which is described as "pleasant."
Lestrange, Bellatrix Black:
walnut, 12 3/4", unyielding,
Taken from her by Ron Weasley at Malfoy Manor, who Disarmed her using Wormtail's wand. Since Mr. Ollivander identified it so precisely, it seems likely that he originally made the wand (DH23, DH24).
Longbottom, Neville's wands:
first one (obtained prior to September 1991 [Y11], broken June 1996 [Y16])
new one (July 1996 [Y16]) cherry, unicorn tail hair
Neville's original wand was his father's old wand and meant a great deal to his grandmother Augusta (his father's mother). This wand was broken by Antonin Dolohov during the battle of the Department of Mysteries in June 1996 [Y16].
Ollivander, Garrick : Hornbeam and dragon heartstring, twelve and three-quarter inches, slightly bendy (Pm)
chestnut, 9 1/4", brittle,
Made for him by Mr. Ollivander (who was forced to do so) and in the end taken from him by Ron Weasley by main force rather than by magic (DH23, DH24).
Riddle, Tom Marvolo (Voldemort):
yew, 13 1/2", single
phoenix tail feather (from Fawkes)
Harry's and Voldemort's wands are "brothers" because they have cores of not only the same substance but from exactly the same source. When they are forced to fight each other, the Priori Incantatem effect is produced. Yew trees are known for their long lives. They symbolize death, but also resurrection. (JKR)
Umbridge, Dolores' wand
While not identified specifically, Umbridge's wand was described as "unusually short." Umbridge herself is unusually short, and perhaps her wand's characterisitcs suggest that her magical ability comes up wanting as well. We never do see her perform any particularly effective magic spells, after all.
Weasley, Ron's wands:
first one (obtained August 1991 [Y11], broken 1st September 1992 [Y12]): ash
new one (31st August, 1993 [Y13]): willow, 14", unicorn tail hair (PA3)
Ron's original wand was a hand-me-down from his older brother Charlie. It was made of ash (see note). This wand broke when the flying Ford Anglia crashed into the Whomping Willow on the 1st of September, 1996 [Y12]. See also entry for Pettigrew, Peter.
"Yeah," said Hagrid, glancing up, too. "Listen, I'm glad we've run inter yeh, Ronan, 'cause there's a unicorn bin hurt -- you seen anythin'?"
Ronan didn't answer immediately. He stared unblinkingly upward, then sighed again.
"Always the innocent are the first victims," he said. "So it has been for ages past, so it is now."
The willow wand is the second wand, the wand that was specifically purchased for him with part of Mr Weasley's winnings from the Daily Prophet contest. As for Ron's original wand, Rowling said the following on her website:
I gave Harry a wand made of holly wood back in 1990, when I first drafted chapter six of Philosopher's Stone...Some time after I had given Harry his holly-and-phoenix wand I came across a description of how the Celts had assigned trees to different parts of the year and discovered that, entirely by coincidence, I had assigned Harry the "correct" wood for his day of birth. I therefore decided to give Ron and Hermione Celtic wand woods, too. Ron, who was born in the February 18 - March 17 period, was given an ash wand (I think I had originally marked him down for beech)...
Rowling is talking about the time before the first book was finished, when she was planning the series. So she is saying that the wand Ron had at the beginning of the stories was made of ash. This was the wand that broke at the beginning of book two and which was replaced at the beginning of book three with a wand made of willow.