In each Formula 1 Grand Prix there are 3 practice and 1 qualifying sessions. Two 1 1/2 hours free practice sessions are held on Friday (the only exception is Monaco in which these sessions take place on Thursday) and in the first one teams are allowed to include drivers (test pilots) that do not form the team duo of regular pilots.
The other two sessions are held on Saturday. The first Saturday session is also a free practice one but it has only one hour and the second, also with 1 hour duration, is the qualifying session in which places in the starting grid are defined. A pilot that wants to be eligible to start a race must participate at least in one of the Saturday sessions.
The qualifying session is divided in three parts. In the first one – Qualifying 1 or Q1 – all the cars (currently 24) may run laps in a 30 minute period. The 7 worst qualifiers are dropped out and will occupy places 18th to 24th accordingly to their best times. After a 7 minute break, the remaining 17 cars may participate in qualifying 2 that has a 15 minute duration. Again the 7 worst drivers will be left out of qualifying 3 and will take places 11th to 17th in the order of their best times. Then, after a 8 minute break, the 10 remaining drivers will struggle with each other for pole position in a 10 minute session. Even if a driver does not complete any lap in qualifying 1 he will be entitled for 10th place except if he had incurred in any action that stewards consider as illegal or if certain components of the car were unduly changed since last race (e.g. gear box or engine). The type of tyres used by drivers when they set their time in Q3 must be the one with which they start the race (unless, for instance, due to the change in weather conditions, other type of tyres should be used for safety reasons).
If any driver in qualifying 1 records a time that is above 107% of the best time registered in that session he will not be allowed to start the race unless the stewards, for instance under exceptional circumstances (which could include setting a suitable lap time in a practice session) allow it otherwise. Should there be more than one driver accepted in this manner, the grid order will be determined by the stewards.
If the stewards consider that a driver has stopped unnecessarily on the circuit or has impeded another driver during qualifying, his times may be cancelled and will start the race in the end of the grid. The cases already mentioned (undue gear box or engine change), as well as unfair driving in previous races, may force a driver to go back on the grid (for instance 5 or 10 places) no matter of his qualifying time.