SeLaLib; Modular library for the kinetic and gyrokinetic simulation of tokamak plasmas by the semi-lagrangian method. In the context of the French Action Fusion (Action d’envergure Nationale Fusion) and a longstanding collaboration between the CEA-Cadarache (French Atomic Energy Commision), the Tonus INRIA Project Team based at the University of Strasbourg and the Max-Planck-Institut für Plasmaphysik (IPP) in Garching, we are currently developing the Selalib library. Selalib is a collection of interfaces and implementations of individual building blocks that can help researchers create and test numerical methods, develop new types of simulations, parallelization schemes, etc., either independently or in preparation for making modifications in existing production code such as GYSELA, the CEA’s massively parallel gyrokinetic, full-tokamak simulator. The Selalib project arose from the need of researchers to develop numerical methods with simplified test cases while also having independently tested modules that would facilitate gradual changes in existing production code. While originally envisioned to be specialized on the semi-lagrangian method, the abstractions that we have built can be used with other types of approaches, such as particle-in-cell. Thus far, the development is being kept within an international group of collaborators, but we expect a stable release soon. Stay tuned!