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If that is the only line in your robots.txt file then it really shouldn't accomplish anything. It's like saying, "Hey...all search engines...take note of this....oh forget it, there's nothing to see here." I agree with Dave...try to fetch the page in Webmaster tools (Google Search Console). You can also use the Webmaster Tools robots.txt tester which often will tell you if there are issues. Hi this is what we thought but Google has not indexed any pages How old is the site? It can take weeks for a new site to get indexed and then to get ranked as well. Do you see any pages on a site: search for your domain? (i.e. site:example.com). This might sound silly, but are you sure that there is no noindex tag on the page?