Dressing up in costumes and masks is one of the best known Purim practices. In the days leading up the holiday, the streets of Jerusalem fill with children attired as Queen Esther, long-sidelocked Chasidim, IDF generals and Justin Bieber. Interestingly the custom is relatively recent. It is thought that dressing up on Purim originated among Italian Jews of the 15th century. The first mention of the practice in halachic writings appears to be in the responsa of Judah Ben Eliezer Halevi, a prominent Venetian rabbi of that time.
Profound theological explanations for dressing up on Purim have developed. The main line focuses on hiddenness as a leading theme of the holiday. God is hidden in Megillat Esther. His name does not appear but God's guiding hand directs the narrative. The Jews of Shushan, and Esther in particular, hid their identity and were forced to reveal themselves. Hitchapsut, the Hebrew for dressing up, means to look for oneself. In searching for what is hidden we find our authenticity.