Synthetic oligonucleotides are an exciting class of therapeutic products that are under development for a variety of indications.Many of them have been developed to address significant medical needs that are so far unmet.Characterization and quality control testing are required throughout the clinical development of oligonucleotides intended for therapeutic use.Detailed information on structural characterization studies that supports the designation of these properties or characteristics should be provided in submissions to regulatory agencies worldwide.What to control is one of the key questions in connection with regulatory submissions during clinical development and marketing authorization applications.This presentation will provide an overview about the regulatory landscape for oligonucleotides.Issues related to the pharmaceutical quality of oligonucleotides are highlighted.Since the early and open communication with Regulatory Agencies can significantly reduce time to market for a new drug product ways of interaction are exposed.