In quantum field theory, in principle Feynman's rules provide a complete solution to the problem of computing scattering amplitudes for sufficiently small values of coupling constants. In practice, Feynman perturbation theory becomes essentially unusable beyond the very simple processes. In the last two-three decades new methods have been invented for the complicated scattering processes in gauge theory and gravity. In this talk we will make a short review on these modern techniques then we will discuss our method which is based on the worldline formalism for tree- and loop-level amplitudes on- and off-shell. At the end we will shortly discuss our recent results in strong field QED (QED in strong constant electromagnetic background fields).