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Gross - that is the worst feeling to see that kind of drop for a client. I would need a look at your GA data for landing pages/keywords from Search Consule to accurately diagnose. But, here are some solid threads to chase: Google Knowledge Graph - We saw this when Google added graph answers for medical terms for one of our clients. Action: do the search incognito to see if Google Graph screwed you. GA tracking broken - make sure there isn't anything odd with your filters, check an unfiltered account. I have seen interns accidentally filter out a part of site or subdomain. Relaunch issues around 404 pages. Use MOZ to track your top traffic keywords. Falling off of SERP 1 / Page 1 can cause this kind of drop Seasonality - make sure you are looking at year-over-year, if the keywords are seasonal it could be normal. IE Christmas traffic is going to drop in Jan... Hope that helps, feel free to post some more data and I can take a look. GL!