My wireless has been set to “inactive”, how do I reactivate it?

I seem to have inadvertently deactivated my wireless in the "Network" section of System Preferences. When I go to the Airport icon in the menu bar it looks like a semicircle that, when clicked on, says "Airport: Not Configured". When I go to configure it, the status is shown as "Inactive", with no "Activate" button in sight. How can I get my wireless working again?

The toggle to make a network adapter active/inactive is somewhat hidden. Select the AirPort adapter, then click the button that looks like a gear at the bottom of the list. This will open a dropdown and you can select "Make Service Active":