Abstract The yellow stingray, Urobatis jamaicensis (Cuvier, 1816) is the most common elasmobranch encountered in the coastal waters of Southeast Florida. The objectives of the present research were to characterize the reproductive biology of a stable population distributed near the northern extent of the species range. Morphological analyses were conducted to determine the seasonal variation of macroscopic and microscopic development and structural organization of reproductive organs of male and female rays (excluding ovarian histology) during all stages of reproduction. This is the first study to document a seasonal biannual cycle for any elasmobranch, as well as, sexual synchrony with a protracted and overlapping periodicity of both reproductive cycles. In male rays, spermatogenesis corresponded with bimodal patterns of genital duct structure, sperm density and linear sperm aggregate formation and disaggregation. Combining data from individual females on: follicle development, ovulation, embryonic growth, and parturition identified the periodicities of the repetitive cycles with ovulation and parturition coinciding from January through April (Feb-Mar peak), and July through October (Aug-Sep peak). Basal crypts were continuously present and supplied the pre-ovulatory synthesis and secretion of histotroph. The basic structure of U. jamaicensis trophonemata was similar to other myliobatiform rays, however, two consecutive endometrial cycles of regeneration and regression were completed with extensive remodeling of glandular and vascular tissues that supplied nourishment and accommodated the respiratory demands of developing offspring. Additional support for concluding there is a biannual cycle was provided by differences in both fecundity and lateralization of uterine function between each reproductive cycle. Oviducal gland structure was reduced and modified with several zone-equivalents, however, secretory products were continuously available and a delicate encapsulating membrane was produced. The uterus was identified as a potential site of fertilization. Extensive levels of matrotrophic input were provided by a modified form of lipid histotrophy with an estimated increase in organic weight from uterine ova to term stage embryos of 4490%. This dissertation is separated into six chapters with (Chapter 1) representing a general introduction and (Chapter 2) describing the materials and methods used throughout the study. The following three chapters represent the bulk of the study, and are divided to characterize the reproductive biology of U. jamaicensis; (Chapter 3) periodicity of reproductive cycles, male anatomy and spermatogenesis, and fecundity patterns; (Chapter 4) uterine morphology, glandular and vascular patterns during the endometrial cycle, and matrotrophic relationships; and (Chapter 5) oviducal gland morphology, sperm distribution throughout the female reproductive tract, determine the occurrence of sperm storage, and describe alternative sites of fertilization. Extensively detailed text and figures further supporting the conclusion of a biannual cycle of reproduction in this animal is provided throughout this dissertation as well as condensed in summary form in the final section (Chapter 6).