Anders Pinzke Estimating the Electromagnetic Chiral Lagrangian Coefficients Master of Science thesis Abstract In the low energy region chiral perturbation theory including virtual photons is used to derive the structure of the generating functional. The work we do is performed within the three flavor framework and reaches up to next-to-leading order. An Euclidian cut-off is introduced to separate the long- and short-distance contributions. The long-distance part is evaluated in the ChPT framework up to $\mathcal{O}(p^4)$. The short-distance part is achieved partly from the work of J. Bijnens and J. Prades, through perturbative QCD and factorization. A matching is made and the finite parts of the low-energy constants (LECs) is determined by using already existing data of the QCD LECs up to order $p^4$. LU TP 04-22