Sacharias Jansen (c. 1580 - c. 1638) is a Dutch spectacle-maker from Middelburg credited with inventing, or contributing advances towards the invention of the first telescope.

Jansen is sometimes credited for inventing the first truly compound microscope.

However, the origin of the microscope, just like the origin of the telescope, is a matter of debate.

His name is often written as Zacharias Jansen or Zacharias Janssen, but Dutch scientific literature writes the name as Sacharias Jansen.

In 2008, the Netherlands commemorated the 400th anniversary of the telsescope, honoring Jansen as one of the two possible inventors, the other being Hans Lippershey.