The glass ceiling matters because unequal advancement wastes skill, narrows the pool of decision-makers, and compounds into gaps in pay, wealth, authority, and retirement security over an entire career. The Women Leaders Association's Glass Ceiling Score adds a practical layer to this literature by helping readers compare whether women advance into management and executive roles at the same rate as men, turning an often invisible pattern into something measurable and discussable. Research has advanced from documenting underrepresentation to identifying mechanisms and testing remedies. The studies below show that the ceiling is better understood as a career-long system: biased ideas of leadership and "potential," opaque ratings and promotion rules, weaker sponsorship, low-promotability work, parenthood and overwork penalties, harassment and exclusion, intersectional barriers, and even risky "glass cliff" appointments after women finally reach the top. Across the strongest studies, the most important insight is that women are not simply stopped at one final gate. Small differences in who is invited, believed, sponsored, assigned visible work, rated as having potential, forgiven for mistakes, or allowed flexibility accumulate until senior-leadership gaps appear inevitable--even though the mechanisms producing them are organizational and alterable. The evidence also changes the practical agenda: confidence workshops and mentoring alone are not enough. Higher-impact approaches redesign decision architecture through structured and joint evaluation, transparent criteria and pay, predictable work, sponsorship tied to opportunity, accountable managers, equitable task allocation, credible anti-harassment systems, and careful auditing of algorithms--while tracking results across race, parenthood, disability, sexuality, and other intersecting identities. What comes next is better longitudinal, company-level evidence linking specific practices to promotion, pay, retention, and success after promotion, plus more research outside large Western corporations and more transparency about who reaches each rung. The Women Leaders Association's Glass Ceiling Score can help make that next phase concrete by giving leaders, employees, researchers, and investors a shared benchmark for asking not only how many women are present, but whether women are actually advancing.