The Hyphen War (in Czech, Pomlčková válka; in Slovak, Pomlčková vojna—literally "Dash War") was the tongue-in-cheek name given to the conflict over what to call Czechoslovakia after the fall of the Communist government.
The official name of the country during the last 30 years of Communist rule was "Czechoslovak Socialist Republic" (in Czech and in Slovak Československá socialistická republika, or ČSSR). In December 1989—a month after the Velvet Revolution—President Václav Havel announced that the word "Socialist" would be dropped from the name, and the country would be known as the "Czechoslovak Republic"—its official name from 1920 to 1938 and from 1945 to 1960. However, Slovak politicians felt this diminished Slovakia's equal stature, and demanded that the country's name be spelled with a hyphen (e.g. "Republic of Czecho-Slovakia" or "Federation of Czecho-Slovakia"), as it was spelled from Czechoslovak independence in 1918 until 1920, and again in 1938 and 1939. President Havel then changed his proposal to "Republic of Czecho-Slovakia"—a proposal that did not sit well with Czech politicians who saw reminders of the Munich Agreement.
As a compromise, on 29 March 1990 the Czechoslovak parliament resolved that the country's long name was to be spelled without a hyphen in Czech (Československá federativní republika) and with a hyphen in Slovak (Česko-slovenská federatívna republika). This solution was found to be unsatisfactory, and less than a month later, on 20 April 1990, the parliament changed the name again, to the "Czech and Slovak Federative Republic" (Czech: Česká a Slovenská Federativní Republika, Slovak: Česká a Slovenská Federatívna Republika, or ČSFR).
The compromise required even more linguistic wrangling than first appears. Generally, only the first word of a country's name is capitalized in Czech and Slovak. Capitalizing all of the words eliminated prestigious problem of whether to capitalize "Slovenská".
Although the Slovaks were demanding a hyphen (Czech, Slovak: spojovník), the Czechs called it a dash (Czech, Slovak: pomlčka). Although there is a clear difference between a hyphen and a dash in Czech and Slovak spelling (a hyphen is used to mark a connection between two words, while a dash is used in other cases), Czechs usually use the term pomlčka for both; Slovaks differentiate them. Nonetheless, English language media generally refer to the conflict as the "Hyphen War".
While the Hyphen War was not really deserving of the name "war", it demonstrated that there were differences between Czechs and Slovaks regarding the identity of their shared country. Over the following two years, more substantial disputes arose between the two halves of the federation. In 1992, Czech and Slovak politicians agreed to split the country into the two states of the Czech Republic and the Slovak Republic—the so-called Velvet Divorce—which became effective on 1 January 1993.
- Československá federativní republika, Sbírka zákonů, Ročník 1990, Částka 19(PDF), page 362, "Ústavní zákon 81/1990 ze dne 29. března 1990 o změně názvu Československé socialistické republiky", 29 March 1990 (Czech) (Constitutional law about the change of the name of the Czechoslovak Socialist Republic)
- Česko-slovenská federatívna republika, Zbierka zákonov č. 19/1990,  page 362, "Ústavný zákon 81/1990 Zb. z 29. marca 1990 o zmene názvu Československej socialistickej republiky", 29 March 1990 (Slovak) (Constitutional law about the change of the name of the Czechoslovak Socialistic Republic)
- Sbírka zákonů České a Slovenské Federativní Republiky Ročník 1990, Částka 21(PDF), page 402, "Ústavní zákon 101/1990 ze dne 18. dubna 1990, kterým se mění a doplňuje ústavní zákon č. 100/1960 Sb., Ústava Československé federativní republiky, a ústavní zákon č. 143/1968 Sb., o československé federaci", 18 April 1990 (Czech) (Constitutional law about the change of the name of the Czechoslovak Federal Republic)
- Česká a Slovenská Federatívna Republika, Zbierka zákonov č. 21/1990, page 404, "Ústavný zákon 101/1990 Zb. z 20. apríla 1990 o zmene názvu Česko-slovenskej federatívnej republiky", 20 April 1990 (Slovak) (Constitutional law about the change of the name of the Czecho-slovak Federal Republic)