Kozhnitz is the name of a Hasidic dynasty founded by the Kozhnitzer Maggid, Rebbe Yisroel Hopsztajn. Kozhnitz is the Yiddish name of Kozienice, a town in present-day Poland.
Rebbe Yisroel Hopsztajn, the founder of the Kozhnitz dynasty, and one of the three "patriarchs" of Polish Hasidism, was a disciple of Rebbe Elimelech of Lizhensk (Rabbi Elimelech Lipman of Lizhensk), author of Noam Elimelech. The Rebbe Elimelech was a disciple of the Rebbe Dovber, the Maggid ("preacher") of Mezeritch, the primary disciple of the Baal Shem Tov, the founder of Hasidism.
The current Kozhnitzer Rebbe of Tel Aviv Rabbi Shimshon Moshe Sternberg (a grandson of Rav Yisroel Elozor) is one of the last Hasidic Rebbes remaining in the mostly secular Tel Aviv, does outreach (kiruv) work there.