A software modem, commonly referred to as a softmodem, is a modem with minimal hardware that uses software running on the host computer, and the computer's resources (especially the central processing unit, random access memory, and sometimes audio processing), in place of the hardware in a conventional modem.

Softmodems are also sometimes called winmodems due to limited support for platforms other than Windows. By analogy, a linmodem is a softmodem that can run on Linux.

Softmodems are sometimes used as an example of a hard real-time system. The audio signals to be transmitted must be computed on a tight interval (on the order of every 5 or 10 milliseconds); they cannot be computed in advance, and they cannot be late or the receiving modem will lose synchronization.