Switching between applications?

I really hate to admit my ignorance, but...
How do you switch between tasks with just the keyboard? I know there is a shortcut, but I can't find any information anywhere about how. I thought it was something like "Ctrl + Tab". I need to be able to switch between open applications on a machine that does not have a mouse and the main application is a "full window" and won't shrink to let you access another open application. Suggestions welcome.