There are many reasons why you might choose to audit a course in college. When you audit a course, you take the course but don't receive a grade or credit; auditing can be as simple as simply listening to the lectures, or as complicated as participating in group work, tests, and following the textbook and assigned readings. Depending on your strategy, auditing a class can be a great way to save money, expand your field of interest, test your interest in a new subject, squeeze in an extra course without the burden of coursework, meet like-minded people, or simply enjoy learning for learning's sake.
Different colleges and universities have different policies and processes of auditing a course. The process of auditing for enrolled students can entail simply asking the professor for permission to sit in on the course, signing up online independently, or formally asking for permission in writing from the department head and/or professor. Sometimes there is no fee to audit a course, and sometimes the fee for auditing the course can be as much as it would be to take the class for credit. Audited courses will be added to your transcript, but they won't be graded.
Even if you are not an enrolled student, it is still possible to audit classes. First, request course catalogs from nearby universities. Make a list of interesting courses and their professors. Armed with this information, get in touch with the registrar to find out how you would go about auditing the class. Depending on the college, the course, and the professor, you might need to obtain special permission or pay some kind of course fee.
So why do all this work to audit a course if you won't receive recognition for it? Your answer to this question depends on your philosophy regarding education. For time-strapped college students on a deadline, audited courses can have several benefits. First of all, auditing a course allows you to soak up new information that can be relevant to your major, concentration, or intellectual formation in general, but without the need to write papers or prepare for tests. Audited courses can be a type of light coursework that you can work on only when you have the time. Maybe you've always had a passing interest in Renaissance painting, but can't see yourself writing a paper on Michelangelo when you should be studying for Organic Chemistry. For very popular courses, auditing can be a way of taking the class if you weren't able to enroll for credit. For very difficult classes that you want to ace, auditing them the year before you want to take them for credit can ensure that you're familiar with the concepts and coursework when there's a grade on the line. For people who are not in college, auditing a course offers the chance to brush up on a specific topic, explore an unfamiliar one, or learn a new skill without having to enroll in a degree program.