If you're ready to take the challenge of covering 26.2 miles, why not do it with the best? Train with Runner's World, the worldwide authority on training and racing for more than four decades. This 16-week program will help you cross the finish line fit and injury-free. It is geared for those who have run for at least a year, three to four times per week on average. Each week features three days of running at an easy pace, a long run, and three days of rest. The long runs, which many rookies dread from the get-go, start at just eight miles and gradually build to 20 miles a week toward the end of the program.