The building sector is responsible for 30% of anthropogenic greenhouse gas (GHG) emissions (UNEP, 2009). Recent energy efficiency measures have helped reduce the operational carbon related to the use phase of the building, but a lack of industry attention hinders the reduction of embodied carbon related to the rest of its lifecycle: material extraction, transport, construction and demolition. Tall buildings are an evident solution to fight urban sprawl and hence reduce transportation emissions. In addition, the volume-to-surface ratio lowers the need for heating and thus reduces the use of operational energy. However, the challenge with current tall buildings is their inherent need for more structural materials. Research is needed to achieve structural efficiency in tall buildings by reducing the material quantities and choosing low carbon materials. For example, we can use mass timber to achieve skyscrapers that sequester carbon. Major engineering companies have studied the possibility of constructing timber skyscrapers. A new timber tower construction technique was recently validated, using reinforced concrete only for the connections. In composite structures, materials are used where they are most needed by combining their best qualities such as fire safety, high strength, and low density. This allows structural engineers to design using less material. This paper makes two contributions: it discusses the challenges of assessing the embodied carbon of timber materials and it characterizes the specificities of tall timber systems with built case studies.