Review: Keep your mind clean by looking over your system periodically

GTD is about having a system that lets you keep your mind clean. This way you can focus in getting things done. The only way to trust your system is keeping it up to date. And this means you have to review it periodically.

You must review your GTD lists as often as you need to, to get them off your mind.

David Allen, Getting Things Done: The Art of Stress-Free Productivity

You should spend enough time daily reviewing your system so that you feel comfortable with what you are doing at every moment.

Weekly review

In addition to the informal practice of daily reviewing your system, GTD recommends a core practice called the Weekly review. Once per week you should review your whole GTD system and do it in a systematic way:

This is the mechanism that will let you keep clear, clean, current and complete.

Most people feel best about their work when they've cleaned up, closed up, clarified, and renegotiated all their agreements with themselves and others. Do this weekly instead of yearly.

David Allen, Getting Things Done: The Art of Stress-Free Productivity