I first give a brief review of covariant chiral perturbation theory (ChPT): the main issue - various solutions and relation to other popular methods like lattice QCD. Then a covariant baryon ChPT with explicit delta degrees of freedom will be applied to study elastic pion-nucleon scattering up to the leading one-loop order. Phase shifts given by the recent analysis of Roy-Steiner equations are well described and the involved low-energy constants are determined. Application of covariant ChPT to a heavy-light system, in particular, interactions between charmed D mesons and Goldstone bosons will be also discussed. In combination with unitarization approach proposed in previous literature we calculate the S-wave scattering lengths and compare them to the ones of lattice QCD. In the end, I conclude with some considerations on what possible new knowledge can be gained using covariant ChPT.