Building capacities in the baseline methodology and assessment of greenhouse gas reductions and sequestration benefits of Clean Development Mechanism (CDM) projects are keys to the successful implementation of the CDM. This guidebook is aimed at addressing these important issues and to assist project developers in establishing baselines for CDM projects following important guidelines. Determining a good baseline will go along way to ensuring the project results in “real, measurable, and long term benefits related to the mitigation of climate change”.The guidebook takes the reader through basic concepts, the processes of developing baseline and baseline methodology, and approval of new baseline methodologies. It presents indicative methodologies for small scale CDM projects and examples of approved methodologies for project specific baselines. Furthermore, it describes the process of developing baseline for land use and land use change CDM projects.The chapters of the guidebook cover:key CDM project criteria, eligible projects, and CDM baseline concepts and methodologya tool for the assessment of additionality for large scale CDM projectssmall scale CDM (SSC) projects, covering guidelines for SSC and SSC categories, simplified baseline methodologies for SSC, and the process of submission of new project categoriessteps for establishing baselines for large scale CDM projects. This includes the use of approved baseline methodologies, as well as a description of the steps taken in developing a new baseline methodologyafforestation and Reforestation (A&R) CDM projectsapproved baseline methodologies for grid connected power generation projects, solid waste management projects and industrial process improvement projects.The guidebook also contains a glossary of key terms most frequently used in context of CDM and specifically baselines, as well as anappendix which presents some key models that could be used for estimating the emissions from emissions reduction projects and sequestration by A&R CDM projects.