The Arduino Wire library is used for I2C communication. These pages will explain how to use it:

• Common mistakes
• Explanation of the functions of the Wire library
• Check for bus errors ?
• Adding a checksum (is almost useless)
• Buffer size of the Wire library
• Arduino in Target mode
• Tricks that are (almost) allowed

Hardware related:

• How to make a reliable I2C bus.
• How to unlock a stuck I2C bus.

Nick Gammon wrote an excellent tutorial about I2C and the Arduino Wire library: www.gammon.com.au/i2c

The I2C bus was created by Philips and that part of the company became NXP. In 2021 NXP changed the names for I2C devices to "Controller" and "Target". The "Controller" controls the I2C bus and generates the clock signal. The "Target" is for example a sensor.

2022: These pages need a update. Too many people see the I2C bus as a communication bus, and too many projects fail when a I2C bus is used between Arduino boards.