From the UK, Eurolines - the overseas wing of National Express - offer return fares to Lisbon, changing in Paris. There are six buses a week to Lisbon from Paris and services to other destinations in Portugal.
Eurolines' routes stretch from Scandinavia to Central Europe to North Africa and journeys to Portugal can be booked in many European cities.
Busabout provides tickets in increments of 2, 3 or four weeks for most European cities on its hop-on hop-off network.
Busabout also offers Flexipasses allowing various days' travel within a set period and its main routes into Portugal are to Lisbon and Lagos in the Algarve from many European cities. There are reductions for passengers under 26.
There are a variety of bus options from Spain into Portugal from Madrid, Seville and Granada with Eurolines and Busabout or with local operators: AutoRes, Alsa (Spain) & Eva (Portugal).
Portugal's domestic bus services are on the whole quicker than a similar journey by train, though they can be more expensive. The networks of the private bus companies cover most of the country's main towns and more local destinations. Departure times can be early in the morning and services are reduced at weekends. Check with the tourist information center for departure points and with the bus companies for schedules.
Express buses can be booked online with Rede expressos or by SMS by calling 969 50 20 50 (information in Portuguese).
Expressos - are the quickest inter-city buses.
Rápidas - are fairly fast regional buses.
Carreiras - are slow local buses.
For more information on driving in Portugal click here
Bus Services in Europe
PortugalVisitor.com - Your Guide To Portugal & Madeira