There is a lot to talk about with both these systems, but I'll give you a short answer as I have experienced it, having used both systems. Passive houses are focused mainly on energy use whereas LEED is more focused on overall green design. The Passive House system analysizes energy consumption and promotes a series of techniques for solving energy loss. I sometimes think of Passive House design as similar to backpacking. In pack backing, in order to carry as little on your back as possible the saying goes: "take care of the ounces and the pounds will take care of themselves." In Passive House design, the models focus on energy transfers between materials that many, even professionals, don't think about, but that really count in the overall energy loss of a home. For instance, the loss through framing members can be huge, regardless of what insulation is used between them. The standards in Passive House design for a tight (but well ventilated) building are very high. Passive house design also addresses issues that can result from a super insulated home, such as mold. LEED is a more all inclusive green design rating system, giving points for site location, transportation, recycled and salvage materials, indoor air quality and other things besides energy efficiency. Their energy efficiency standards are not as strict as Passive House standards. LEED rated buildings deal with the many things that go into building with environmental consciousness. LEED stands for Leaders in Energy and Environmental Design. The buildings are meant not only to be successful energy efficient and environmentally conscious design, but also didactic, in that they teach people what is possible for success in this area.