While the United States leads the world in many measures of health care innovation, it has been suggested that it lags behind many developed nations in a variety of health outcomes. It has also been stated that the United States continues to outspend all other Organisation for Economic Co-operation and Development (OECD) countries by a wide margin. Spending on health goods and services per person in the United States, in 2007, increased to $7,290 - almost 2(1/2) times the average of all OECD countries. Rising health care costs in the United States have been estimated to increase to 19.1% of gross domestic product (GDP) or $4.4 trillion by 2018. The increases are illustrated in both public and private sectors. Higher health care costs in the United States are implied from the variations in the medical care from area to area around the country, with almost 50% of medical care being not evidence-based, and finally as much as 30% of spending reflecting medical care of uncertain or questionable value. Thus, comparative effectiveness research (CER) has been touted by supporters with high expectations to resolve most ill effects of health care in the United States and provide high quality, less expensive, universal health care. CER is defined as the generation and synthesis of evidence that compares the benefits and harms of alternate methods to prevent, diagnose, treat, and monitor a clinical condition or to improve the delivery of care. The efforts of CER in the United States date back to the late 1970's even though it was officially born with the Medicare Modernization Act (MMA) and has been rejuvenated with the American Recovery and Reinvestment Act (ARRA) of 2009 with an allocation of $1.1 billion. CER has been the basis for health care decision-making in many other countries. According to the International Network of Agencies for Health Technology Assessments (INAHTA), many industrialized countries have bodies that are charged with health technology assessments (HTAs) or comparative effectiveness studies. Of all the available agencies, the National Institute for Health and Clinical Excellence (NICE) of the United Kingdom is the most advanced, stable, and has provided significant evidence, though based on rigid and proscriptive economic and clinical formulas. While CER is making a rapid surge in the United States, supporters and opponents are expressing their views. Part I of this comprehensive review will describe facts, fallacies, and politics of CER with discussions to understand basic concepts of CER.