Please note that the following information is only a guide.

BASICS
Since the founding of the Czechoslovak Republic on October 28, 1918, and until September 30, 1949, citizenship by birth was determined by the citizenship of the father. Persons, whose father was Czechoslovakian citizen upon their birth, became Czechoslovakian citizens as well. Czechoslovakian citizens from Transcarpathian Ukraine who resided in Transcarpathian Ukraine when it became part of the USSR, became Czechoslovakian citizens if they opted for Czechoslovakian citizenship between June 29, 1945 and April 1, 1946. Persons originally from Transcarpathian Ukraine, who resided in Czechoslovakia prior to June 29, 1945, became Czechoslovakian citizens automatically. Women with foreign citizenship, who married a Czechoslovakian citizen, became automatically until July 23, 1947 Czechoslovakian citizens.

DETAILS
Czechoslovakian state citizenship first appears with the founding of the Czechoslovak Republic on October 28, 1918. Citizenship was governed by Act No. 236/1920 Coll., on Czechoslovakian state citizenship (in force until September 30, 1949), which drew on laws from the Austro-Hungarian Empire and on post-First World War international agreements.

The following persons became Czechoslovakian citizens on October 28, 1918:

- as of October 28, 1918, persons who at the latest as of January 1, 1910 held a continuous domiciliary right on that part of the territory of former Austro-Hungarian Empire, which subsequently became Czechoslovakia (domiciliary right was confined to a particular municipality and was acquired by birth, marriage, acceptatnce, or assumption of public service);

- former German citizens who resided on the territory which formerly was part of Germany and became Czechoslovakia (Hlučínsko region);

- former German, Austrian, and Hungarian citizens who were born on the territory of Czechoslovakia as children of German citizens with residency on this territory or as children of Austrian and Hungarian citizens with domiciliary right on this territory;

- as of October 28, 1918, persons who formerly held a domiciliary right in a municipality in that part of the territory of former Austro-Hungarian Empire which later did not become Czechoslovakia and who became public officials or employees of a state company in Czechoslovakia;

- persons born on the territory of Czechoslovakia without a proof of foreign citizenship;

- persons who opted for Czechoslovakian citizenship;

- persons who requested that Czechoslovakian citizenship be confered upon them;

- persons who were not confered with Yugoslavian citizenship;

- some persons with domiciliary right in a municipality in that part of the territory of former Austro-Hungarian Empire which was ceded to Italy.

Between 1918 and 1949, Czechoslovakian citizenship was obtained by one of the following:

Birth
- if a child was born into a marriage and the father was Czechoslovakian citizen;
- if a child was born outside of marriage and the mother was a Czechoslovakian citizen.

Marriage
- automatically until July 23, 1947 (when the law changed) and by request thereafter.

Option
- according to the post-First World War peace agreements;
- persons from the Volyně region - Soviet citizens of Czech or Slovak nationality living on the territory of the former Volyně governorate had a right to opt for Czechoslovakian citizenship until May 15, 1947 and to resettle in Czechoslovakia;
- persons from Transcarpathian Ukraine - hitherto Czechoslovakian citizens residing in Transcarpathian Ukraine when its territory became part of the USSR on June 29, 1945, had the possibility to opt for Czechoslovakian citizenship until April 1, 1946;
- army personnel of Russian or Ukrainian nationality joining the Czechoslovak Army during the Second World War and their family members had the option to become Czechoslovakian citizens;
- Czechoslovakian citizens from Transcarpathian Ukraine who resettled in Czechoslovakia remained Czechoslovakian citizens, as well as persons who between June 29, 1945 and September 1945 (i.e. when the border agreement between Czechoslovakia and the USSR came into force) moved from Transcarpathian Ukraine to Czechoslovakia.

Declaration of fatherhood
- if the parents married after the birth of a child and the father, with the consent of his wife and before two witnesses, declared his fatherhood.

Special regulations
- according to post-First World War peace agreements;
- denial of foreign state citizenship according to post-war peace agreements (Yugoslavian and Italian);
- Presidential Decree No. 33/1945;
- reemigration;
- resettlement from Hungary.

Ex lege
- former Hungarian state citizens who before January 1, 1910 were of age and resided for at least four years in a municipality in Slovakia or Transcarpathian Ukraine, were entitled, upon fullfilment of certain criteria, to Czechoslovakian citizenship.

Naturalization

Act No. 236/1920 Coll., on Czechoslovakian state citizenship, was in force until September 30, 1949. Regulations for acquiring Czechoslovakian state citizenship described here were thus applicable only until that date. As of October 1, 1949, new legislative act governing citizenship came into force - see the respective chapter.

Dual Citizenship
Agreement between Czechoslovakia and the United States of America on prevention of dual citizenship was in force from November 14, 1929 until August 20, 1997. The agreement was suspended between September 17, 1938 and May 7, 1957, when either Czechoslovakia or the United States were in the state of war (i.e. from the first Czechoslovakian mobilization until establishment of diplomatic relations with Japan). The agreement prevented dual citizenship of Czech (Czechoslovakian) citizens, who became naturalized in the United States, and vice versa, of citizens of the United States, who became naturalized in Czechoslovakia. Only persons 21 years and older were subject to this agreement.