The switch to right hand traffic in Czechoslovakia describes changes in the rules of the road in 1938/1939.
Before 1938, Czechoslovakia drove on the left. In about 1925, Czechoslovakia accepted the Paris convention and undertook to change to right hand traffic "within a reasonable time frame". In 1931, the government decreed to change over within 5 years, which did not happen. The main obstacles were financial cost and widespread opposition in rural areas. In November 1938, parliament finally decided to change to right hand traffic with effect from May 1, 1939.
(Austria had already been forced to switch after its 1938 annexation by Germany.)
The occupation of the Protectorate of Bohemia and Moravia by Germany on March 15, 1939, sped up the change. A few places switched the same day (e.g. Ostrava), the rest of the area of the Protectorate on March 17, and Prague got a few more days to implement the change and switched on March 26.
Tramway infrastructure in Prague had been modified since November 1938. In the final days there were daily reminders of the change in newspapers and large warnings were painted on the streets and on tramway cars. Drivers adapted quickly and only a small number of traffic accidents happened due to the switch with only one recorded fatality in Prague.
Right hand traffic had already been introduced in Slovakia by a decree of the government of "autonomous Slovakia" within Czechoslovakia in late 1938. Buses in the capital Bratislava were adapted in 1939, and the last roads in Slovakia switched to the new system in 1940/1941.
The area which is now Southern Slovakia was occupied by Hungary then and so would not have changed until Hungary changed in 1941.