Please note Session Two 2008 rule changes in blue below.
Please note original 2008 rule changes and clarifications in maroon below.

General Rules

Each regular season match consists of two equal halves of 24 minutes.
A two-minute half-time period will occur between halves.
Teams may call one one-minute timeout per half (when in possession of ball, ball out of play).
There is no overtime, injury time or stoppage time.
Teams are comprised of four outfield players and one goalkeeper.
A team must have four players to begin a match. No team may have fewer than three players on the pitch at any time.
The goalkeeper must wear a different color jersey than the outfield players.
All players must wear the following: shirt, shorts, shinguards, socks, sneakers -- no exceptions.
No casts or splints are allowed.
Jewelry and earrings and other items are not permitted.
There is no sliding in futsal (see goalkeeping exception below).
There is no offsides in futsal.
There is no contact in futsal. Although some contact is unavoidable, what is important is that a player not make physical contact with an opponent prior to making contact with the ball. In addition such legal contact shall not be excessive or use disproportionate force.

Substitutions

All substitutions are on the fly, this includes goalkeeping substitutions. Referees will not stop play for goalkeeping substitutions. Coaches are requested to change goalkeepers during halftime, during timeouts and after the opposing team scores.
A substitute may not enter the match until the player leaving the match is at the touchline. Coaches are asked to have players slap hands at the touchline to ensure that no more than five players are on the court at once.
All substitutions must take place in front of the teach bench -- not at the half-way line.
All U13 and older divisions will switch ends and switch benches at the beginning of halftime, ensuring that all substitutions take place in the defensive half.
All U12 and younger divisions will remain at the same bench but will defend the same ends, ensuring that all substitutions take place in the defensive half, unless the match official(s) deems an advantage gained by defending one end, in which case the teams will switch benches.

Restarts

Kickoffs: are indirect (at all ages). The ball must be played forward first.
Kickins: are indirect. The ball must be placed on the line and the kick must be taken within 4 seconds. The kicker's plant foot must be out of bounds or on the line. (A kickin that goes directly in the opposing goal is a goal clearance for the opposing team. A kickin that goes directly in the defensive goal is a corner kick of the opposing team.)
Goal Clearances: are taken in place of goal kicks. The goalkeeper must use his hands to roll, bounce or throw the ball from anywhere inside the penalty area to anywhere in his own half outside the penalty area. The ball may not cross the half-way line without first being touched by the ground or another player. (At U15 and older, goalkeepers may throw the ball directly across the half-way line. In these leagues, goal clearances are indirect. A ball thrown directly into the opposing goal results in a goal clearance for the opposing team.)
Corner Kicks: are direct. The ball must be placed directly on the corner spot and the kick must be taken within 4 seconds.
Free Kicks: may be indirect or direct. The ball must be stopped completely before the kick may be taken.
Penalty Kicks: are taken from the penalty spot and must be shot at goal by a clearly identified kicker. Defenders may not be nearer to the ball than 15 feet and must be behind an imaginary line running from touchline to touchline even with the penalty spot.
Distance: For all of the above, except goal clearances, opponents may not be closer to the ball than 15 feet.
Ceiling: If the ball hits the ceiling or other object, the team that did not touch the ball last restarts play with a kickin from the nearest point on the touchline.

Fouls and Misconduct

Indirect Free Kicks: When a player plays in a dangerous manner, impedes an opponent (without playing the ball), prevents the goalkeeper from releasing the ball with her hands, commits any offence for which play is stopped to caution or eject a player.
Direct Free Kicks: When a player kicks or attempts to kick an opponent, slides or slidetackles (automatic yellow card/caution) an opponent, jumps at an opponent, charges at an opponent, strikes or attempts to strike an opponents, pushes an opponent, holds an opponent, spits at an opponent, touches the opponent while attempting to win the ball, handles the ball deliberately.
Yellow Card / Caution: The offending player serves three-minute penalty (all ages/divisions). If opposing team scores within three minutes, any other player may replace the offending player. If the goalkeeper is cautioned, an outfield player may serve the three-minute penalty. If a substitute is cautioned, the team must remove an outfield player for a three-minute penalty period.
Red Card / Ejection: The offending player must leave match and facility. The offending team plays down for five minutes unless scored upon before the five-minute penalty expires. The offending player serves a minimum one-match suspension.
Accumulated Fouls / AFPK: All penal fouls are recorded on the scoresheet and on the scoreboard. If red fouls blue a sixth time in one half, for that sixth penal foul and all subsequent penal fouls in that half, blue is awarded an accumulated fouls penalty kick. If the foul occurs farther from the attacking goal than the second penalty spot, the AFPK is taken from the second penalty spot. If the foul occurs nearer to the attacking goal than the second penalty spot (but outside the penalty area, of course), the attacking team may choose whether to take the AFPK from the second penalty spot or from the spot of the foul.  All AFPK's must be shot at goal by a clearly identified kicker. The defending team may not make a wall and may not be nearer to the ball than 15 feet and must be behind an imaginary line running from touchline to touchline even with the spot of the kick.  The goalkeeper may be off her line, but may not be nearer than 15 feet from the ball. Accumulated fouls are reset to zero at the beginning of the second half. 
Second Penalty Spot: 30 feet from the center of the goal
Penalty Spot: 20 feet from the center of the goal
Advantage: Advantage will be applied in futsal (FIFA amendments for 2007), but penal fouls will still count as accumulated fouls.  If the referee shouts, "play" and gestures with both arms, the foul was a penal foul and will be counted accordingly.  If the gesture is with one arm, the free kick would have been indirect and thus does not count toward the total.

The Goalkeeper

Must wear a different color shirt. May wear long pants and/or other padding.
Is the only player who may slide, but only when sliding in his own penalty area and only when playing the ball.
May receive a kickin directly.
May kick the ball directly over the half-way line.
At U15 and older, goalkeepers may throw the ball directly across the half-way line. In these leagues, goal clearances and other distributions are indirect. A ball thrown directly into the opposing goal results in a goal clearance for the opposing team.
May score directly with his feet during the run of play.
May not punt or drop-kick the ball. Ball must settle to the ground or be touched first, no "air" under the ball when kicked.
May not possess the ball for more than four seconds in her own half.