Ovulatory follicle development and associated oocyte maturation involve complex coordinated molecular and cellular mechanisms not fully understood. This study addresses, for the first time in any species, the relationships among diameter, vascularization, follicular-fluid factors, and gene expression for follicle growth, steroidogenesis, angiogenesis and apoptosis in granulosa/cumulus cells and oocytes during different stages from the beginning of largest/ovulatory follicle to impending ovulation. Follicle dynamics was tracked and follicle-wall blood flow evaluated daily through transrectal ultrasonography in mares. The largest follicle of the ovulatory wave was distributed in six diameter groups (predeviation, deviation, postdeviation, early preovulatory, preovulatory, and impending ovulation) according to the targeted diameter for complete aspiration and cell harvesting. The most remarkable findings were (i) positive association between follicle development, blood flow, intrafollicular FSH, LH, estradiol, progesterone, and mRNA expression for FSHR and LHCGR in granulosa cells of largest/ovulatory follicle; (ii) plateau/decrease in follicle diameter, blood flow, and granulosa cell mRNA for FSHR, LHCGR, IGF1R, VEGFR2, CYP19A1, and CASP3 at the preovulatory stage; (iii) higher StAR and BCL2 and lower CASP3 mRNA in granulosa cells at impending ovulation; (iv) greater IGF1R mRNA in the granulosa cells at the predeviation stage; and (v) lower FSHR, LHCGR, IGF1R, and VEGFR2 mRNA in cumulus cells, and greater LHCGR and IGF1R mRNA in oocytes at the ovulatory stage. This study is a critical advance in the understanding of molecular mechanisms of follicle development and oocyte maturation and is expected to be vital for future studies targeting potential markers for follicle selection, development, and ovulation.