Single quotes ex: '' and Double quotes ex: "". The single qoutes allow for 2 escape characters: \' and \\ . The double qouted string literal allows for many different escaped special characters (like \n is a line break) and allows for string interpolation, or the injection of evaluated Ruby code into the string ex: "Hello #{my_name}". The single qouted string takes up much less memory than a doulbe qouted string with interpolation. Without interpolation, both are about the same.