Interaction region diagnostics in $e^{+}e^{-}$ ring colliders

We present a review of diagnostic tools intended to control and optimise the beam overlap in the interaction points of both symmetric and asymmetric colliders. Practical applications of some methods a dopted to tune the impact parameter at LEP are described. An experiment is proposed to investigate the relation between the coherent tune split between the s- and the p- modes of oscillation and the i nchoerent beam-beam parameter under different operational conditions.