If you're looking to brush up on specific skills or enter a new field, online courses are one of your most affordable options; Right now, you can enroll in a handful of Harvard University courses for free. edX, an e-learning non-profit, was founded by Harvard and MIT. It has dozens of free online courses from both Ivy League institutions, as well as many other top schools and companies. Below, you'll find nine Harvard University data science courses that you can take together as part of a cohesive data science certificate program ($792) or individually for free (with one-off paid certificate options available as well).