The Rules

Overview

To start the match, a coin toss determines the side to serve first. The side to serve first alternates in subsequent games.
Switch sides of the court after every game.
The side that wins the point serves the next ball.
A player can let the ball bounce or hit it straight out of the air from anywhere on the court.
A side scores a point if the other side hits the ball out, fails to return a ball, or commits a fault.

The server can stand anywhere on their side of the court to serve.
The receiver can stand anywhere on their side of the court to receive the serve.
After the server hits the serve, it must bounce on the server's court before going over the net.
The receiver must let the serve bounce on their court before returning it.
Exception: If the receiver is standing behind the non-volley line (7 feet back from the net), they can volley the serve.
The serve is the only time a player may hit the ball onto their own court before it goes over.

Games are played to 10 points; win by 2.
Sets are played to 50 points. Each game counts for 10 (even if the final score is 11-9).
Example: Side A has won 3 games; Side B was won 1 game. The set score is 30-10.

Doubles moonball follows the same rules as singles with a few additional rules.
At the beginning of the match, each pair decides on an "even" server and an "odd" server.
When the side to serve has an even number of points, the even servers serves. When they have an odd number of points, the odd server serves.
Example: If the score is 5-4 for the serving side, their odd server will serve.
There are no restrictions on where players can stand during the serve. However, the "no-volley" rule still applies on the serve.
In open play (after the serve), players can volley the ball from anywhere. This means that one partner can stand right at the net to attempt to block the ball.
Each side is only allowed one ball contact to get the ball over the net. The ball cannot be passed to the partner.

Touching the net during gameplay with any part of the body is a fault.
Impeding the arm swing or follow-through of a player at the net is a fault.
Hitting the ball twice is a fault.
Exception: if the ball contacts the player's body multiple times within the same overall motion, no fault is committed.

A player may play the ball around the net post and back into the opponent's court.
If the ball bounces on the opponent's court, then bounces backwards (by spin or by wind) back over the net, the opponent must touch the ball for the return to count.
Incidental contact: If the ball makes a minor contact with the player's body before the player hits the ball, the return counts as long as the player did not intentionally use that body part to hit the ball.
For example, the ball bounces in front of the player, then bounces up and hits them in the chest, and then they hit it back over the net. This counts as a valid return.
However, if the ball rebounds off the player's body and flies away, they may not run to hit it back over the net. This is a double contact fault.