The climb of Teide requires a written permit. Officially, this is in order to reduce environmental impact on the summit area. It seems like the park authority thinks that the best way to accomplish this is to make the permit very difficult to obtain. More on this below.

The following post is an extract from an article by  Petter Bjørstad http://www.ii.uib.no/~petter/mountains/3000mtn.html#teide

Thanks to a very good description by Endresen, we had little difficulty. For completeness, we essentially repeat his description here (Credit for the 3 next pictures is all his). First, go to the main city on Tenerife, Santa Cruz de Tenerife (north-east on the island).

Locate Plaza de Espana with the Town Hall

There is a large underground parking garage just south with access from a street that runs from the sea and uphill. Walk across the lower end of the plaza away from the tower. Your view should look like this

Continue straight ahead until you locate the fourth road going left. This street is Calle Emillio Calzadilla, there is a Bang and Olufsen store on this corner. The street number is 5, this is the third numbered access on your left side of the street. The door looks like this

There is not a single sign indicating that you are at the right place, quite incredible. The office is located on the 4th. floor (counting from zero), ring the bell. When we were there, nobody bothered to open despite repeated, intense ringing. The office is supposed to be open from 0900 to 1400 on ordinary weekdays.

(The complete address is: ICONA, Office P.N. de Teide, Calle Emillio Calzadilla 5, 38002 Santa Cruz de Tenerife. Phone numbers: 922290129 or 922290183).

Fortunately, somebody exited the door thereby providing us access. At the 4th. floor there is a sign telling you that you have indeed found the National Park office. The person behind the desk will immediately ask for a photo copy of your passport. He is, in fact, not interested in the original. There is no photo copy service available, thus it is important to know this and bring a copy with you.

The permit is free, one person is designated the leader and the passport data for additional people in the party is written down on the permit form. Perhaps even more unreasonable, you are asked to specify the date and a precise two hour interval in which you intend to climb from the top station of the cableway to the summit. I asked if the permit could allow for say, two different days, but no. If we did not climb in the specified two hour slot, then we could always come back to the office and secure a new permit!

We picked the next day, March 2nd. and estimated that the interval from 1300 to 1500 would allow for a reasonable climb to the top station. All members of your party must bring their passports on the climb, the idea being to check this information and the permit as you reach the top station of the cableway