This paper reviews the basic principles of vacuum sewer systems and the introduction of vacuum sewers to Canada. A vacuum sewer uses air pressure instead of gravity as the driving force for waste water transport. Waste water is moved in plugs, separated by air gaps, at high velocities through small diameter pipes. The pressure differential of about one-half atmosphere is created by a central vacuum pump. Specially designed vacuum toilets, valves, and a central collection tank complete the system. The advantages of a vacuum sewer system over a conventional gravity system are its ability to transport waste water horizontally and to a certain extent upgrade, its much lower water usage, and its lower capital cost. However the length, capacity, and lift potential of vacuum sewers are limited by the available pressure differential, which precludes their use in many cases.