My paper aims at examining the real composition and workings (as opposed to normative existence) of Istanbul mahalles in the early seventeenth century mainly on the basis of court records and mühimme defterleri. (Istanbul sicill defterleri, 1-6, mühimme defterleri, 75-82) Urban mahalles of central Ottoman has been viewed as rather homogeneous, tightly-knit, and relatively unchanging. To have a fresh look at those apparently stable Ottoman mahalles, one may want to observe mahalles of a city for a particular time of distress in order to see what kind of problems they were faced with and in what ways they handled the problems. The early seventeenth century was exactly such a period in Istanbul, as the city was flooded with immigrants that included more non-Muslims than Muslims, water and food supply for the residents ran short, and numerous reports were made about the robbers and outlaws in and around the city. Expulsion cases and complaints arising from the mahalles in this period were mostly related to issues of morality and security. They tend to talk about prostitution and robbery as well as possibility of fire and/or murder. I plan to examine such cases involving mahalles with following questions in mind: 1. Who filed complaints against whom and who expelled whom within the mahalle? There are cases where coreligionists expelled coreligionists, Muslims expelled non-Muslims, and Mixed people of a mahalle expelled some non-Muslims. I will analyze the leadership structure and the concerns raised in each case with a view to understanding Muslim/non-Muslim relations of the time . 2. What are the implications of such expulsion cases/complaints in regard to the phenomenal migration to Istanbul in those days? Does the fact that expulsion cases mostly talk about issues of morality and security and usually not about the lack of kefalet indicate that newcomers were accepted if they obeyed the norms of the mahalle and be useful to the existing residents? 3. Why were there repeated government orders to keep the mahalles better-defended with gates and/or guards at least since the late sixteenth century and well into the 1660s? Did something make at least some of the mahalles reluctant to be totally protected from outsiders? Were the level and nature of protection wanted by the government different from those wanted by the people of the mahalles?