More complex than it looks, here’s how to make a Wave Pattern in Illustrator
Learn how to create a wave pattern in Illustrator. You will see how to draw the starting shape and how to fill it. You will learn how you can test it to see how it will look and then adjust it if necessary before continuing.
You will use the Shape Builder tool to build the actual pattern starting piece and the new Pattern feature in Illustrator CS6 & Illustrator CC to make the repeating pattern swatch.