With the consolidation of fathers' engagement in caregiving, understanding the neuroendocrine and hormonal mechanisms underlying fatherhood becomes a relevant topic. Oxytocin (OT) has been linked with maternal bonding and caregiving, but less is known about the role of OT in human fatherhood and paternal caregiving. A systematic review of methods and findings of previous OT research in human fathers was carried. The literature search on PubMed and Scopus yielded 133 records. Twenty-four studies were included and analyzed. Significant variability emerged in OT methodology, including laboratory tasks, assessment methods, and outcome measures. Fathers' OT levels appear to increase after childbirth. OT was significantly correlated with less hostility and with the quality of paternal physical stimulation in play interactions, but not with paternal sensitivity. Fathers' and children's OT levels were significantly correlated in a limited subset of studies, intriguingly suggesting that cross-generational OT regulation may occur during the early years of life. This study highlights relevant issues and limitations of peripheral OT assessment in human subjects, especially in fathers. Although the study of paternal neuroendocrinology appears promising, coping with these issues requires dedicated efforts and methodological suggestions are provided to guide future advances in this field.