Arduino family of microcontrollers has become an integral part of the world of electronics. Users of Arduino range from makers to enthusiasts to professionals. Therefore, it is not surprising that a large number of books on the different aspects of application and programming of Arduino are available. This is not another book on these aspects. I would like to deal with interrupts, which make the execution of the Arduino program more effective. Some years ago I published the book "Arduino: Hard- und Software Open Source Plattform" (ISBN 978-3-907857-16-8) in German language. From my readers, I know that the section covering interrupts is seen as an important complement to the widely available basics. This was the base for writing this booklet which explains the usage of the interrupts of the ATmega328 based Arduino. I tried to look behind the scenes of the Arduino environment. Various program examples with interrupts have shown how the resources of the microcontroller used can also be accessed at the register level.