The objective of the Open Planning of Sanitation Systems approach is to provide a practical guideline for the planning and implementation of sanitation projects based on sanitation system function requirements rather than technologies. This shall improve the sustainability of sanitation systems. Sanitation systems can be regarded as sustainable if they protect and promote human health, do not contribute to environmental degradation or depletion of the resource base, and are technically and institutionally appropriate, economically viable and socially acceptable – furthermore, they have to remain functional over time. The OPSS planning process itself is performed in five steps that are briefly explained. The planning and implementation tool is based on the Open Comparative Consequence Analysis methodology that has been developed in Sweden by WRS Uppsala AB. The approach itself was established by EcoSanRes.