The Deutschland-Ticket is valid on all means of regional and local public transport across the whole of Germany. Ticketholders have unlimited use of all forms of public transport, from buses and trams to city trains, underground trains, suburban trains, regional trains, regional express trains in 2nd class, and many ferry lines.
The D-Ticket is not valid on long-distance services (e.g. Deutsche Bahn’s IC, EC, ICE, but also RE lines provided by DB Fernverkehr AG) or on privately operated services (e.g. FlixTrain, FlixBus). In addition, the D-Ticket is not valid on primarily tourist or historical means of transportation.