There are three main schools of the tea ceremony which are called the Sansenke. This name comes from Sen no Rikyu also called Rikyu Sōeki who was the great grandfather of the founders of the three main schools. They are said to be the main schools because of the bloodline connecting them to the grand master of the tea ceremony Sen no Rikyu, and because they have the biggest following of students. All three Sen family schools apply "Sen" in the name of their school

Urasenke

Probably the school with the biggest following among the Sansenke is Urasenke. This school was established by Sen Sōshitsu (1622-97) who also inherited the teahouse named Konnichian. The current head of Urasenke-Konnichian-foundation is Iemoto Zabōsai Genmoku Sōshitsu. The name Urasenke comes from various parts; "Ura" comes from the location of the Konnichi-an teahouse which faces the back street. In Japanese, back is called "ura". The "senke" part of the name means "house of Sen". So, altogether it is the "house of Sen on the back street". Officially the name of the tea house is also included which means the full name is Urasenke-Konnichi-an.

Omotesenke

The second biggest school of the japanese tea ceremony is Omotesenke. Omotesenke school of tea was established by Koushin Sousa (Kōshin Sōsa) (1613-72) who also inherited the teahouse named Fushinan. The current head of Omotesenke-fushinan-foundation is Iemoto Sōsa Jimyosai. The name Omotesenke comes from the following Japanese; "Omote" comes from the location of the Fushin-An teahouse which faces the front and main street. In Japanese, "front" is called "Omote". The "Senke" part as in both Urasenke and Omotesenke means the "house of sen". Due to its location this school is the teahouse on the front street.

There are some differences during the tea ceremony performed by Urasenke and Omotesenke. For example, Urasenke whisks the Macha strongly so that the froth is covered with a layer of foam. Omotesenke has some foam on top of the tea too but leaves, what is referred to as a "lake", in the center open and free of foam.
Omotesenke uses Susudake which is smoked-bamboo or darkened-bamboo for its Chasen, while Urasenke prefers to use blank, untreated bamboo for its Chasen.
Some people say that Urasenke likes to display and show-off its most valuable and expensive utensils to impress its guests. Utensils made by famous craftsmen or expensive brand tools are said to be preferred by Urasenke. Omotesenke however, prefers to keep things simple and plain. This does not mean that cheap junk is used to perform the Japanese tea ceremony, but that more consideration is given to balance various utensils so that they will each receive adequate attention and won't be overlooked.

Mushanokōjisenke or Mushanokoujisenke

The smallest of the Sansenke is Mushanokōjisenke school of tea. Mushanokōjisenke school of tea was established by Ichiou Soushu(Ichiō Sōshu) also a great-grandson of Sen no Rikyu. The current head of Mushanokojisenke-Kankyuan-Foundation is Iemoto Rikyu Koji, a fourteenth generation direct descendant of Sen no Rikyu.
Mushanokojisenke's name comes from the street it faces, which is the Musha no Koji Dori. (Dori means street in Japanese)

Source: http://japanese-tea-ceremony.net