It was a season which featured a lot of dramatic races including 4 rain-affected races in Portugal, China, France and Great Britain. It also saw the domination of Valentino Rossi with 16 podiums out of 17 races and 11 wins, beating Marco Melandri by a distant 147 points in the championship. In the 125cc Thomas Lüthi won the World championship dramatically, when Mika Kallio's teammate Gábor Talmácsi overtook Kallio at the last corner in Qatar. Kallio would have got five points more, and then points would be 242–242, but Kallio would have won the title with more wins (4-5).
A new 'flag-to-flag' rule has been introduced. This means that, in the event of rain, the race will not be stopped and instead will be allowed to change bikes. This rule will only count for the MotoGP class.
A new white flag has been introduced. If this flag is waved at a marshal post during the race, all riders are allowed to change bikes.
Changes have been made to the starting procedure. Unless the race is interrupted, after the leading rider has crossed the finish line at the end of his first lap, the riders are not allowed to change their bikes in the MotoGP class. If a race has been declared 'wet', riders are allowed to change a bike equipped with a rain tyre to a bike with an intermediate or slick tyre or vice versa, or from a bike equipped with a slick tyre to a bike equipped with an intermedia or rain tyre is allowed at any time during a race. However, if a race has not been declared 'wet', the change of bikes are only allowed after the new white flag is shown around the circuit. In both cases, aids such as tyre warmers, the replacement of tyres and general adjustments are allowed on the bike in the pits. During the ride through the pits, all riders must respect the speed limit of 60 km/h from the start to the end of the sign. In the pits, overtaking is forbidden and any rider who breaks this rule will be fined 100 U.S. Dollar for the first offence and 500 U.S. Dollar for ensuing offences at the same place. Any rider who breaks this rule during a race will be penalised with a ride through penalty. In the case of an infringement, the Race Direction must communicate the offence to the team of the rider after having received the information. The rules will not be changed for the 125cc and 250cc classes.
All races will be categorised as either 'wet' or 'dry'. A board might be displayed on the grid to show the current status of the race. If no board is displayed, the race is automatically considered 'dry'. The purpose of this classification is to indicate to all the riders the consequence of varying conditions during the race.
An update has been made to the yellow flag rule. In case of danger, riders must already slow down, be prepared to stop if needed and are forbidden to overtake until the green flag is shown. If this rule is infringed upon, the lap time of the rider will be cancelled. New in this case is, in case of a violation of the rule during the race, the rider must return to his position prior to his pass. The penalty will first be communicated to the team, who then displays a board for the rider on the finish line during a maximum of three laps. If the rider does not go back to his previous position after the board has been shown to him three times, he will be penalised via a ride through penalty. In both cases, further penalties such as a fine or suspension can also be implemented. If a rider realises that he did an infraction immediately after having overtaken another rider, he must raise his hand and let the rider(s) past that he had overtaken. If he does this, no penalty will be imposed. During the final lap of inspection, this flag must be waved at the exact place where the flag marshal will be placed during the practices and races.
A new age limit will come into effect for the 125cc class. From now on, the minimal age of entry for the class will be 19 years and 21 weeks old.
A limit will be imposed on the maximum number of team personnel on the pit lane. The maximum number of team personnel per rider in the pits has been limited to four for all classes.
Each team which is a member of the IRTA must submit an entry for their team by the 28th of February of the year in question. An exception is made when special dispensation is granted, which is valid for all races in the FIM Road Racing World Championship Grand Prix. At the same time, the team must specify the designated riders and the class in which they will participate, as well as the circuits used for testing designated by teams in the 125cc and 250cc classes.
Practice restrictions have been introduced. Contracted teams and their designated riders who profit from a Participation Agreement to take part in the MotoGP class are forbidden from practicing at any circuit from 1 December of one year and 20 January of the next year, both dates being inclusive. Contracted teams and their designated riders who profit from a Participation Agreement to take part in the 125cc and 250cc classes may only participate in winter testing (tests between the end of the season and the first event of the following season), at circuits in the continental zone where the team is located (Europe, Asia/Oceania, Africa and the Americas).
Contracted teams and their designated riders who profit from a Participation Agreement in any class are forbidden from practicing:
- at any circuit included on the calendar of the current year after the date that is fourteen days prior to the start of the first race of the season.
- at any circuit included on the calendar of the cuttent year during "breaks". A break is defined as 'two consecutive weekends where events are not scheduled'. The period of the break begins from 09:00 on the Wednesday after the last grand prix until the following grand prix.
The following exceptions will apply to the rule:
- Free practice or qualifying practice at the event.
- Practice at any circuit after the event at that circuit except during a break.
- Official practice sessions organised by the IRTA.
- Practice by contracted teams and their designated riders who profit from a Participation Agreement to participate in the 125cc and 250cc classes, at the two testing circuits appointed by each team which may take place up to fourteen days before the scheduled race for the circuit, except for when there is a break.
Practice restrictions do not apply to wild card riders. An exception is made to a practice session or race at any circuit within fourteen days of a race.
This rule was additionally added on the 30th of August 2005:
A change has been made to the start procedure if a race has been interrupted. In case of a normal start, the riders will now only be allowed to do a single warm-up lap ahead of the restart instead of the previous two.
All fuel tanks must be filled with material that is fire retardant or be lined with a fuel cell bladder. All fuel tanks made out of any metallic material such as steel, aluminium and so on, must be filled with material that is fire retardant or be lined with a fuel cell bladder. In the MotoGP class, all fuel tanks made out of any composite material such as carbon fibre, aramid fibre and so on, must have passed the FIM standards for fuel tanks and be lines with a fuel cell bladder. Any fuel tanks made out of composite material must have a label verifying that it conforms to the FIM Fuel Tank test standards. These labels must include the fuel tank manufacturer's name, the take of the tank manufacturer and the name of the testing laboratory. Full details of the standards are available from the FIM.
The fuel tank capacity for all four-stroke bikes will be reduced from 24 to 22 litres.