Heart failure with preserved ejection fraction (HFpEF), which currently represents approximately 50 % of heart failure (HF) cases, is common and associated with high morbidity and mortality. Understanding the epidemiology of HFpEF has been difficult due to the challenges in HFpEF diagnosis and the heterogeneous etiologies and pathophysiologies that underlie HFpEF. Nevertheless, several high-quality epidemiology and observational registry studies of HFpEF demonstrate that an increasing prevalence of HFpEF in both the outpatient and inpatient settings, coupled with a lack of evidence-based effective treatments for HFpEF, is resulting in an emerging epidemic of HFpEF. In this review, we discuss the emerging HFpEF epidemic, focusing on: (1) reasons for the rising prevalence of HFpEF; (2) the abnormalities in cardiac structure and function that dictate the transition from risk factors to HFpEF; (3) novel HFpEF mechanisms that may underlie the increase in HFpEF prevalence; (4) prognosis of HFpEF; and (5) risk prediction in HFpEF. We conclude with 10 unanswered questions onHFpEF epidemiology thatwill be important areas for future investigation.