How It Works - Testing is done via a saliva sample.  Results are ready in 6 – 8 weeks.
Your DNA results are compared against 31 distinct populations worldwide.
Approximately ten million customers have been tested as of 5 February 2020.[1]
Matching occurs at 1 segment of 7cM and 700 SNPs.  Additional segments match at 5cM and 700 SNPs.[2]
Performs an automated phasing technique called Finch to determine if the DNA is from the maternal or paternal side.  They break the cMs into 100 marker segments of 50 to 400 segments per chromosome which is compared to their reference populations.  A confidence threshold is then applied to determine ethnicity percentages.[3]
7% of users have family trees.
Browsing raw data - 23&me's instructions
Downloading Raw DNA. - prepared Fall 2015
Reviewing matches. prepared Fall 2015
Uploading a Gedcom.  prepared Fall 2015
2017 Salt Lake Christmas Tour Presentation and Speech 
Founded in 2006.  Began autosomal testing in 2007 for health and genealogy.
[1] See "A Court Tried to Force Ancestry.com to Open Up Its DNA Database to Police.  The Company Said No," buzzfeednews.com, buzzfeednews.com : accessed 5 Feb 2020).
[2] Blaine T. Bettinger, “The Family Tree Guide to DNA Testing and Genetic Genealogy,” (Cincinnati, OH : Family Tree Books), 103, 23andMe.
[3] Bettinger, “The Family Tree Guide,” 158, 23andMe.
[4] Gleeson, Maurice and Patient, Michelle, “Where Else to Look?” Unlock the Past Alaska Cruise, 9 Sep 2018.