The prevalence of chronic illness in reproductive-age women is increasing; nearly 40% of them carry at least one diagnosis. Those with chronic medical problems often face significantly more risks in pregnancy than their healthy counterparts, so preparation before conception is even more necessary to optimize pregnancy outcomes for both the mother and the newborn. Contraception provides time for pregnancy preparation, but selecting safe and effective methods from which the patient can choose is often complicated by her health condition, the medications she takes, and any related comorbidities. Studies show that those with medical problems have even more uneven use of contraception than healthy controls have; they may have unintended pregnancy rates above the 45% average for the country as a whole. The US Medical Eligibility Criteria (US MEC) provide evidence-based recommendations for developing the list of options to present to each woman with medical challenges during a patient-centered, shared decision-making counselling visit. This chapter encourages clinicians to focus on all the reproductive health needs of affected women and provides insights into the rationale behind the US MEC to help guide daily practice.