Hey there,

This may be a stupid question, but I was just curious as to whether or not you have to buy a new ticket if you change lines on the metro in Madrid. Thanks!

You don´t have to buy another ticket if you change the line. One ticket is for as many lines as you need.
Just if you go to some far stations (where there´s nothing interesting to see) you have to buy a special tickets. (Metrosur and Rivas, Arganda...)

Hi laura7412
As long as you do not leave the metro system (that is exit to the street), then 1 ticket (aprox 1 Euro), will allow you to move from line to line. Hold on to your ticket though, you will need it to exit the metro system.
When in Madrid, I usually buy a 10-journey ticket (un metrobus de diez)- this one ticket (which costs around 6 Euros) will allow you ten journeys on the metro. You can also use it on the busses.
Of you want to find what others have said about the metro, then do a search on the MadridMan forums using the keywords MADRID METRO.
Hope this helps
Robbieroy
Hope this helps

There is no stupid question, on the contrary I think it is wise to ask about what is unknown to one.

Short answer to your question: No, one ticket is enough, and this is valid for 99% of the trips a tourist can do.

Long answer: The Madrid metro network is actually composed of three sub-systems, and has three different fares:

One is the Southeastern leg of line 9 (Puerta de Arganda-Arganda del Rey). This subsystem is operated by TFM.

The second one is the line 12 in full, plus the two Southernmost stations in line 10 (Joaquin Vilumbrales and Puerta del Sur). This subsystem is called Metrosur.

The last one is the rest of the network, that includes all stations and lines into Madrid city limits. It is called Metromadrid.

If your trip's departing point and destination are not in the same subsystem, you have to use a ticket called 'Combined' and it is 1.30 euro. Else, the ticket to use is a 'Single' one and it is 1.00 euro only. If you want to save money, there are 10-trip tickets that all cost 5.80 euro, but are different for each subsystem. The one valid for downtown Madrid is called Metrobus and it is valid for 10 trips either on Metromadrid, or Madrid buses, or both (i.e., 5+5, or 7+3, or...). There are others for Metrosur and TFM and they cost the same, but are valid only for their respective subsystems.

For a fully detailed explanation about fares, please refer to here , a Madrid Metro Official Website page.

How much is a monthly pass? What is needed to obtain one? For example trips from Leganes to Torrejon de Ardoz.

To have the "Abono transporte" for adults there are no special conditions, you can get it at the moment in the "Estancos" (where you buy cigarrettes), or in any metro station.
There are several zones, the smallest is just the city and it costs 35 euros (zone A), it includes almost all the metro and also the buses that moves through the city.
There are bigger zones (B,C...)that allows you to take buses to some cityes around Madrid. (The biggest one costs 90 euros)
There are also special prices for youg people, but it takes some time to have one of these since you asked for it. (maybe a month)
You cannot go to Torrejon by metro, you have to take a bus

There's actually a new turistic "abono". I couldn't find the page in english.

http://www.ctm-madrid.es/novedades/novedades_detalle_abono.jsp

Ok, 1 more question- do the machines in the metro accept euro bills or do you need change? If change is needed, where is a good place to get it?

The machines accept Euro bills. Try to use the smallest bill possible for your needs as all the change is given in coins. The machines also accept bank debit cards and credit cards (Visa/MC).

There's an English language option on this site which sells the Abono Turístico and Madrid Card: I wasn't able to select it, though (it might be my browser at fault). http://www.neoturismo.com/es/Inicio.aspx.