Here you will find several relevant meta catalogs, which allow you to search multiple catalogs at the same time:
biblioPera
A web portal of eleven research institutes in the area of Beyoğlu/Istanbul with a common library catalog.
KVK
The KVK is a meta catalog for the identification of several hundred million media in catalogs worldwide.
TO-KAT
The national catalog of academic libraries. For technical reasons, not all universities participate. The non-participating universities can be researched in the Yordam catalog (see below).
MENAsearch
the discovery system of the FID Middle East, North Africa and Islamic Studies and at the same time libraries with Middle Eastern holdings in K10+ (ULB Sachsen-Anhalt, UB Tübingen, SUB Göttingen, SBB zu Berlin, SUB Hamburg, ThULB Jena, UB Freiburg, UB Heidelberg, UB Leipzig, Zentrum Moderner Orient, Berlin (reference library), Orient-Institut Beirut (no interlibrary loan), Orient-Institut Istanbul (no interlibrary loan).
Yazmalar
A directory of manuscripts in Turkey. Meta catalog of currently approx. 30 manuscript libraries in Turkey; simple catalog search possible without registration, with registration page views, etc. The Süleymaniye catalog is not integrated. This catalog provides direct access to digital copies of some of the manuscripts. For this, registration is required. Downloads and prints are charged a fee!