The website of the National and University Library in Zagreb has many interesting online databases such as the OPAC (online public access catalog) of the National Library (Katalog NSK), a union catalog of Croatian libraries (Skupni katalog), and the electronic version of the Croatian national bibliography (Hrvatske bibliografije).
The OPAC, which uses the CROLIST interface, contains records of Croatian books from the National Library since 1981, foreign books or older items acquired since 1984, CIP records (prepublication records) for Croatia, doctoral and masters' theses, printed music since 1976, cassettes and CD's since 1990, maps and atlases since 1850, articles from Croatian journals from 1990, and items received on legal deposit from Former Yugoslavia from 1983-1990. In addition some retrospective conversion of older materials has occurred due to various bibliographic projects like the compilation of a retrospective bibliography of Croatian books. Although the National Library may not hold all of the items that are listed in these retropective bibliographies, the records can still be found in their OPAC.
Besides records for monographs, the database also has information on Croatian and foreign periodicals held by the Library. The interface for the OPAC is available in either Croatian or English. It is possible to search by author, title, keyword or ISSN/ISBN.
The user may limit by language, date or type of material. Croatian diacritics are necessary to search the catalog. When searching without diacritics the catalog may return some results, leading the user to believe that they have exhausted the available material, but performing a search on a name such as Božic will illustrate the problem. Searching this name with and without diacritics will return very different results. Because of the somewhat unusual filing of entries of words and names that begin with letters that require diacritics, browsing the catalog may also lead to some erroneous conclusions.
All this being said this, the catalog is extremely valuable for the Croatian materials included.

The union catalog of Croatia or Skupni katalog also uses a CROLIST interface and includes the holdings of not only the National Library, but many of the major academic libraries of the country, but it is unclear exactly how many Croatian libraries are involved.
There are simple search and advanced search options which allow for the construction of some fairly sophisticated searches. The Croatian version of the website provides statistics on the number of records in the catalog: almost 350,000 monographs, over 106,000 article citations, over 40,000 serial records and about 800 collected works. The entry shown below is an example of a 1988 publication in the union catalog.

The final online resource worth mention at the website of the National Library is the online version of the Croatian national bibliography . All 3 parts, Niz A/monographs , Niz C/serials , and Niz B/articles from Croatian journals, are all present here. The coverage is from 1999 to the present for Niz A, 1998 to the present for Niz B, and from 1997 to the present for Niz C. One can read the printed issues online as it is published, that is, in the classified subject arrangement, or use the various indexes to scan by author or title, etc. See the image below to become familiar with the interface.