F1: a code to compute Appell’s F 1 hypergeometric function. We present the FORTRAN code to compute the hypergeometric function F 1 (α,β 1 ,β 2 ,γ,x,y) of Appell. The program can compute the F 1 function for real values of the variables x,y, and complex values of the parameters α,β 1 ,β 2 ,γ. The code uses different strategies to calculate the function according to the ideas outlined by F.D. Colavecchia et al. [Comput. Phys. Commun. 138, No. 1, 29–43 (2001; Zbl 0984.65017)].