I've copied the EU fact sheet for you.
"In 1992 the ‘third package’ (namely Council Regulations (EEC) Nos 2407/92, 2408/92 and 2409/92, now replaced by Regulation (EC) No 1008/2008 of the European Parliament and of the Council) removed all remaining commercial restrictions for European airlines operating within the EU, thus setting up the ‘European Single Aviation Market’. The latter was subsequently extended to Norway, Iceland and Switzerland. It could be further extended to some neighbouring countries through the ‘European Common Aviation Area Agreement’, provided those countries progressively implement all relevant EU rules — which is not yet the case[1].
The ‘third package’ substituted ‘Community air carriers’ for the national air carriers, and set as the basic principle that any Community air carrier can freely set fares for passengers and cargo and can access any intra-EU route without any permit or authorisation (with the exception of some very particular routes on which Member States can impose public service obligations, subject to conditions and for a limited period of time).
The ‘third package’ also laid down the requirements that Community air carriers must comply with in order to start or continue operations, principally:
They shall be owned and effectively controlled by Member States and/or nationals of Member States, and their principal place of business shall be located in a Member State.
Their financial situation shall be good. They shall be appropriately insured to cover liability in case of accidents.
They shall have the professional ability and organisation to ensure the safety of operations in accordance with the regulations in force. This ability is evidenced by the issue of an ‘air operator certificate’."
Essentially it means that any airline licensed by an EU state can operate to/from or within the borders of any other EU state.