Czech Republic–Slovakia relations
Before 1918, both countries were part of Austria–Hungary. However, after the Ausgleich of 1867 Czechia belonged to the Austrian Empire while Slovakia belonged to the administratively separate Kingdom of Hungary, and between 1918 and December 31, 1992, both countries were part of Czechoslovakia. 
Both countries established diplomatic relations on January 1, 1993. These international relations are usually referred to or described as "very good", "cordial", and "above standard" in the media. When a Czech or Slovak president is inaugurated, very often his first international visit is to the former part of the common country. The same custom applies to newly elected prime ministers of the Czech Republic and Slovakia.
Postage stamps and postal history of Slovakia
After World War I and the dissolution of the Austro-Hungarian Empire, Slovakia and the regions of Bohemia, Moravia, and Carpathian Ruthenia formed the Czechoslovak Republic. From 1918 to 1939, stamps of the Czechoslovak Republic inscribed either "Česko-Slovensko" or "Československo" were used in Slovakia. 
Between 1939 and 1945, the Slovak Republic, a client state of Nazi Germany, issued stamps inscribed "Slovensko".