Composite materials are well known for their high strength-to-weight ratio, but their unique manufacturing process presents some challenges and is a source of geometric variations. To minimize the effects of such variations in the final product is the main goal of geometry assurance. To achieve that, variation simulation tools are used to predict variations and optimize manufacturing parameters, to ensure a robust design. In this paper, the most common variation sources linked to the manufacturing process are discussed. Then, variation simulation tools and features for parts and assemblies are presented. Applicability for composites of existing tools and other studies for metallic parts is compared. Finally, future challenges in variation simulation for composites are discussed.