The Nile Equatorial Lakes Subsidiary Action Program (NELSAP) has initiated an action research project to increase the knowledge base and strengthen the capacity to integrate green infrastructure in river basin planning in three transboundary wetlands: Semliki Delta (DRC-Uganda), Sango Bay-Minziro (Tanzania Uganda) and Sio Siteko (Kenya-Uganda). This project builds upon existing and previous plans and programs and aims to pave the way and create drivers to improve governance, promote conservation and sustainable livelihoods in the Sio Siteko wetland landscape which directly or indirectly involve the wetlands. This Wetland Monograph presents a detailed study of the physical context, biodiversity and ecosystems, policies and institutions, socio-economics and livelihoods, and social dimensions of the Sio Siteko wetland landscape. In addition, it identifies the main challenges the wetland landscape faces and on which to develop successful management plans and investment portfolios, setting the stage for the NELSAP-GIZ project that is reactivating the stalled Sio Siteko Transboundary Wetlands Management Plan developed in 2009. Sio Siteko is part of the Sio-Malaba-Malakisi wetland system and an Important Birding Area (IBA) with over reported 300 bird species, including the endangered Grey Crowned crane and the threatened Papyrus Gonolek. Notable mammals include vervet monkey, otter, sitatunga, hippopotamus and water mongoose. In addition, there are 206 plant, 29 fish, and eight reptile species, among others. The Sio Siteko wetland also plays an important role in regulating the hydrological system and supporting livelihoods through the provision of fish, grazing land and building and craft materials. The main challenges the wetland faces include the massive encroachment of the wetland for cultivation, over-exploitation of wetland resources, and invasive species. The root causes of the challenges are the high population growth rate (2.8% per year), increasing pressure on the wetland resources. Other underlying causes include weak law enforcement and institutional capacity, especially regarding the transboundary aspects of wetland management, poor access to sanitation and waste disposal services and climate change. Water resources are likely to be increasingly strained in the future climatic and socio-economic conditions of the wider Sio Siteko area. Wetlands are an effective sink for carbon, thereby buffering the drivers of climate change and supporting climate resiliency. Sio Siteko wetland landscape needs better protection from human disturbance and climatic changes to protect the ecosystem and local livelihoods. In order to develop successful and sustainable management and investment plans, it is crucial to understand the environmental and socio-economic system of the wetland landscape and the main threats it faces. Therefore, the first step and cornerstone of this approach is this Wetland Monograph, which serves as the baseline and reference for the Sio Siteko Wetland Management and Conservation Investment plans.