We will discuss a direct prescription for computing the mixing among gauge invariant operators in N=4 SYM. This approach is based on the action of the superalgebra on the states of the theory and circumvents the problem of diagonalising the dilatation matrix. As an example, we will derive the leading and subleading planar quantum corrections to the BMN-like operators belonging to the supermultiplet with 2 impurities. Furthermore, we will discuss the relation to Beisert's SU(2,2) dynamic S-matrix approach. The same method can be applied in the BMN limit of the dual string description. The string theory expressions for the states match nicely the field theory ones up to order lambda'. We will also focus on the implications of the mixing terms for 3-point functions of 2 BPS and one non-BPS operator. Namely, should the mixing terms were not there, constraints following from the superconformal and the bonus U(1)Y symmetries would be violated. Subsequently, we will utilise the BMN limit of the AdS5xS5 string theory to analyse the string amplitudes corresponding to the 3-point functions studied above. The mixing is again crucial to ensure the cancellation of various amplitudes that would otherwise violate symmetry constaints. However,on the string side, we find examples of interactions which violate expectations coming from superconformal Ward identities and the U(1)Y symmetry. Finally, we will comment on the possible resolution of this mismatch.