Despite recent success, large neural models often generate factually incorrect text. Compounding this is the lack of a standard automatic evaluation for factuality-it cannot be meaningfully improved if it cannot be measured. Grounded generation promises a path to solving both of these problems: models draw on a reliable external document (grounding) for factual information, simplifying the challenge of factuality. Measuring factuality is also simplified-to factual consistency, testing whether the generation agrees with the grounding, rather than all facts. Yet, without a standard automatic metric for factual consistency, factually grounded generation remains an open problem.We study this problem for content transfer, in which generations extend a prompt, using information from factual grounding. Particularly, this domain allows us to introduce the notion of factual ablation for automatically measuring factual consistency: this captures the intuition that the model should be less likely to produce an output given a less relevant grounding document. In practice, we measure this by presenting a model with two grounding documents, and the model should prefer to use the more factually relevant one. We contribute two evaluation sets to measure this. Applying our new evaluation, we propose multiple novel methods improving over strong baselines. Context Speedway management would maintain their pol-icy to not race on Sundays until 1974 Indianapolis 500-1974. After a heartbreaking loss in 1912 Indianapolis 500-1912, Ralph DePalma succeeds in victory for 1915. DePalma was accompanied by riding mechanic Louis Fontaine. GPT-3 → The 1915 race was the first to have a post-race distance of more than 500 miles GPT-2 tuned → Depalma died on march 31, 1915, at his home in south Pasadena, California, of cancer. Grounding SOUTH PASADENA, Calif., March 31 (AP)-Ralph DePalma, pioneer auto racer who probably won more races than any other driver in history, died today of cancer. His age was 72. GPT-2 LT → He was the first driver to win the World War I-era American championship. GPT-2 PMI-add → Depalma died of cancer at his home in south Pasadena, California, at the age of 72.