Medical Science Liaisons (MSLs) play a vital role within medical affairs, generating and communicating scientific information to stakeholders. From 18-24 months before a product is launched, MSLs can facilitate discussions about unmet need and modes of action for new products. They apply this expertise through to launch and post launch activities, helping ensure access to new therapies for the patients who need them. This White Paper examines the MSL role and how it can support internal and external decision-making processes, leveraging effective communication skills to build relationships and share information, using a stepwise approach to gather insights. The necessary scientific, business and personal competencies are described, along with best in-field practices for supporting an effective and tailored two way dialogue with different stakeholders.