  We compute structure constants in N=4 SYM at one loop using Integrability.
This requires having full control over the two loop eigenvectors of the
dilatation operator for operators of arbitrary size. To achieve this, we
develop an algebraic description called the Theta-morphism. In this approach we
introduce impurities at each spin chain site, act with particular differential
operators on the standard algebraic Bethe ansatz vectors and generate in this
way higher loop eigenvectors. The final results for the structure constants
take a surprisingly simple form. For some quantities we conjecture all loop
generalizations. These are based on the tree level and one loop patterns
together and also on some higher loop experiments involving simple operators.
