This chapter intends to give an overview about the fertility awareness-based methods (FABMs), exploring their current knowledge and raising issues about their use and applicability. The term “Fertility Awareness-Based Methods” (FABMs) groups, under one definition, different methods and approaches through which women can recognize their fertile and infertile periods during the menstrual cycle; this knowledge leads to a conscious choice of having or not unprotected sexual intercourse based on their family planning preferences. Beyond the common core are included in this group older and newer methods, as well as algorithm predicting tools or user-only based methods using several and distinct biomarkers, giving different information: choice can be tailored based upon women’s preferences, reproductive period, and gynecological condition (e.g., breastfeeding, perimenopause, menstrual irregularities). This wide variety needs in-depth study to give proper and consistent information, while knowledge in this field among clinicians worldwide is limited, often partial and misled. Evidence on FABMs suffers from limited strength and overall low quality. Notwithstanding, in the twenty-first century, many published studies showed renewed interest in this field, addressing efficacy issues as well as acceptability, user profiling, satisfaction, and retention rates. FABMs boasts wide applicability, in every culture and socioeconomical status. In the twenty-first century, centrality is given to the 4P medicine, in which the “participatory” dimension stands as a pillar; FABMs fit this need properly, as they are expressions of patient empowerment. Furthermore, the reappraisal of FABMs will unveil their potential in preventive medicine and as possible auxilium in clinical practice.