The outpatient clinic is one of the most important departments of the hospital. Since most elective care trajectories start here, with a consultation between a care provider and a patient, the outpatient clinic functions as a gate to enter the hospital. Outpatient care is evolving rapidly around concentration of low- and high-complex care and the digitization of care processes, thus introducing new challenges in the organization of care. In this chapter we introduce the concept of access and waiting time, briefly discuss outpatient clinic capacity management, study the planning and control framework in place, and discuss Operations Research models for outpatient clinic optimization, specifically those for patient flow analysis and appointment planning. We conclude this chapter with lessons learned during the implementation of our work and discuss current challenges in outpatient clinic management. We specifically aim to support the researcher who is starting in this field, by providing a comprehensive overview of the theoretical and practical aspects of outpatient clinic optimization.