There are numerous bus stations in Kiev and various companies offering services to and from international destinations.
Ecolines operates from the Central Bus Station on Moskovska Square (near Demiivska Metro Station) and offers buses to Kiev from European countries including Austria, Czech Republic, Denmark, Estonia, France, Germany, Hungary, Latvia, Netherlands, Poland, Slovakia, and the UK.
Passengers should note that northerly routes to Moscow and destinations in Latvia and Estonia (Riga, Tallinn etc.) pass through Belarus. Most travellers, with the exception of those holding a CIS passport, will need to obtain a transit visa to pass through Belarus. They are expensive and a pain to apply for.
Eurolines Germany offers regular bus services from many German cities to Kiev and other destinations in Ukraine. Buses stop at the Dachna Bus Station at Peremohy 142 (close to Zhytomyrska Metro Station).