The Zentralkartei Banken (ZentK) is the database where the master data for the institutes with reporting obligations (MFIs, their foreign branches and subsidiaries as well as the multi-office banks) are administered chronologically and therefore their codification in all surveys of the banking statistics. This key information is used uniformly from all units of the banking statistics. Due to the high confidentiality of the data the access for researchers is restricted to a subset of the variables and some of them are provided in less detail than the underlying data. MFIs with legally dependent branches abroad shall be called multi-office banksin the narrow sense. Since panel dataset shall be provided for research if possible and since it is not known in advance whether a specific MFI will set up or acquire a legally dependent branch abroad or will cease to have one a MFI without legally dependent branches abroad shall be called multi-office bank in the wide sense. Multi-office banks in the wide sense and their domestic parts have non-overlapping identifiers. Multi-office banks in the wide sense and their domestic parts often have the same master data but not always. Therefore, in MaMFI the master data for multi-office banks in the wide sense and their domestic parts are stacked. Different from ZentK MaMFI includes a derived variable created by the RDSC that informs whether an institute has acquired or merged with another institute. Mergers are reported not at the legal date but in the month the equity of the absorbed institute shows up in the balance sheet of the absorbing institute. The master data in MaMFI relating to mergers does not fit the banks’ profit and loss accounts well, since for them the legal date of mergers is relevant.