The Synchronous library is a Modelica package to precisely define and synchronize sampled data systems with different sampling rates. It encapsulates the Modelica 3.3 synchronous language elements with an easy-to-use graphical user interface. The library has elements to define periodic clocks and event clocks that trigger elements to sample, sub-sample, super-sample or shift-sample partitions synchronously. Optionally, quantization effects, computational delay or noise can be simulated.