If you have a lot of money or very little, then tax liens can be a great way to get started investing. About half the states offer liens for the public to buy.
Tax liens are a great way for an investor with little money to get in to the real estate market. I often encourage a new student to buy a few liens so that they can start putting dollars to work quickly. The returns are very good, usually between 12% to 18%, and the redemption periods are often two years or less.