Seldon is a C++ library for linear algebra. It provides matrix and vector structures, and functions for computations (linear algebra). It is designed to be efficient and convenient. It includes several types of matrices: full matrices, sparse matrices, symmetric matrices, Hermitian matrices, and triangular matrices. Different storing formats and memory managements can be selected. Seldon is interfaced with Blas (1, 2, 3) and Lapack. For sparse matrices, Seldon is interfaced with several direct solvers (MUMPS, SuperLU, and UmfPack). There are several iterative solvers available such as Gmres, BiCgSTAB, Qmr, etc.