What makes a marathon worth running? A great course, enthusiastic fans and a race that's well-organized are all important aspects. These factors played a big role in helping us rank our list of the world’s best marathons. We first began with some simple statistics from Running USA that identified which 2013 marathons were the largest in the United States and the world (largest meaning races with the most finishers.) We also factored in the opinions of our readers. We asked you, the marathon runners of the world, which 26.2-mile races are your favorites of all time. To tie it all together, we created a scoring system that awarded points for everything from course quality, event organization and fan ratings based off runner reviews on MarathonGuide.com to the number of 2013 finishers and of course, votes and comments from our reader survey. Now, the results are in and these 25 races have been deemed the best marathons in the world.