The use of Ecological Momentary Assessment (EMA) has led to increased insight into borderline personality disorder (BPD) symptoms, especially regarding affective instability. EMA is characterized by a series of repeated assessments of current affective, behavioral, and contextual experiences or physiological processes while participants engage in normal daily activities. EMA has several advantages. It enables researchers to avoid biased recollection, to investigate within-person processes, and to enhance real-life generalizability. This review is dedicated to four main objectives: (1) to discuss the characteristics of EMA in studying BPD symptomatology; (2) to provide an extensive overview of EMA findings in BPD structured into findings regarding DSM-IV criteria and findings regarding emotional dysregulation as stated in the biosocial theory of Linehan; (3) to discuss challenges of EMA and to give recommendations for the proper use of it; and (4) to highlight prospects and promising applications that should be addressed.