This document discusses and compares several medical reference sources and knowledge bases, including Google, PubMed, UpToDate, and Dynamed. It finds that Google is replacing PubMed as a first point of access to medical literature. Studies show clinical questions are more likely to be answered by UpToDate than PubMed. UpToDate was also associated with improved health outcomes and shorter hospital stays. However, other sources like Zynx Evidence and Clinical Resources @ Ovid ranked higher than UpToDate in evidence-based quality in one evaluation. There was no clear preferred choice between UpToDate, MD Consult and Dynamed in a user preference study. UpToDate sees more use than Dynamed at one medical library mentioned.