If nine men are assembled in a room, and a tenth men is outside by the window, can this tenth men be counted so a Minyan can be formed? It is clear that the fellow outside cannot be counted if the window is closed. Even if the window is open but there are security bars running across the area of the window, the man cannot count toward the Minyan. Regarding the case of an open window, different views exist among the Poskim. The Bet Yosef cites Rabbenu Yeruham (1290-1350) as ruling that the fellow outside does not count toward the Minyan, unless he brings his head and the main part of the body through the window. This is the view accepted by the Hayeh Adam (Rav Abraham Danzig, Vilna, 1748-1820). The Bet Yosef then cites the more lenient ruling of Rav Yishak Abuhab (Spain, 14 th century) that it suffices for the person to put his head inside through the window for him to be counted toward the Minyan. Thirdly, the Bet Yosef cites the position of Rav Hai Gaon (Babylonia, 939-1038), brought by the Orhot Haim, that if the man outside "shows them his face" then he may be counted toward the Minyan. The Bet Yosef posits that these final two views actually are the same opinion, expressed in different words, though he is uncertain what this opinion is. It is possible, he writes, that Rav Hai Gaon agreed that the fellow outside must bring his head into the room through the window, but his position was not made clear in the citation in the Orhot Haim. Conversely, it is possible that Rav Yishak Abuhab agreed that it suffices for the person to merely show his face to the people inside, and does not actually have to bring his head through the window. A number of other Rishonim (the Radbaz and Rav Moshe Ibn Habib) ruled clearly that the individual must bring his head inside the room through the window in order to count toward the Minyan, perhaps giving us reason to assume that this was the view also of Rav Yishak Abuhab and Rav Hai Gaon. This question is debated by later Poskim. The Magen Abraham (Rav Abraham Gombiner, Poland, 1635-1682) and the Peri Hadash (Rav Hizkiya Da Silva, 1659-1698) ruled leniently, that nine men in a room can form a Minyan with a tenth man outside a window if he faces them through the window. The Hida (Rav Haim Yosef David Azulai, 1724-1806), in Mahazik Beracha, cites those who require the person to bring his head through the window, and then brings those who rule leniently, that it suffices for the tenth men outside to face the nine men inside. As for the final Halacha, although the Mishna Berura follows the lenient view, the Kaf Ha'haim (Rav Yaakov Haim Sofer, Baghdad-Jerusalem, 1870-1939) ruled stringently, that the person outside must bring his head inside the room to be counted. This is the position followed by Hacham David Yosef, in Halacha Berura, and this is the Halacha according to Sephardic practice. Summary: If nine men are in a room, and a tenth man is outside a window that is completely open, they can form a Minyan if the man outside brings his head inside through the window.