New York City does have an MLS. Its run by the Real Estate Board of New York (http://www.rebny.com/content/rebny/en.html http://www.rebny.com/content/rebny/en.h

New York City does have an MLS. Its run by the Real Estate Board of New York (http://www.rebny.com/content/rebny/en.html http://www.rebny.com/content/rebny/en.html) and is called RLS (REBNY Listing Service). Streeteasy simply never had access to RLS so they had to get their data from other sources, primarily from scraping websites and emails, as well as some direct data feeds from brokerages that agreed to work with them. source: I work in technology in the New York real estate sector.