This thread will serve as a single sticky thread for the REW Forum, providing a common point for REW guides, links, tips, technical articles, and sticky posts. Sticky threads are now indexed here and will float in the normal thread section.
Getting Started with REW, an excellent introductory guide you can download for setting up and using Room EQ Wizard, from AustinJerry and others at AVSForum. This link will always take you to the latest version. (NOTE: This guide suggests positioning the mic at a 90° angle to the speaker, pointed at the ceiling, as is typical for setting up Audyssey and Dirac Live calibrations. However, REW author John Mulcahy and Herb Singleton of Cross Spectrum Labs have long recommended 0° orientation for in-room frequency response measurements of main-channel speakers, and 90° for acoustics measurements.)