Climate finance has evolved into a system that links climate objectives to capital allocation under uncertainty. The chapter traces its development from early negotiations and dedicated funds to integration within regulation, public financial management, and investment planning. It defines core concepts adaptation and mitigation finance, additionality, mobilization, and measurement, reporting, and verification to establish a shared vocabulary. The mapping of actors shows how multilateral and national development banks, climate funds, capital markets, supervisors, and country platforms combine distinct mandates and access pathways. Instruments and channels are examined across grants, concessional loans, guarantees, equity, labelled bonds, results based payments, and blended structures, emphasizing fit with cash flow profiles and verification feasibility. Key challenges include access for vulnerable contexts, disbursement and absorptive capacity, transparent valuation and mobilization, and market integrity. Emerging opportunities center on credible taxonomies, digital verification, adaptive investment methods, and asset level risk analytics. The chapter argues that portfolios scale with integrity when incentives reward verifiable outcomes and accounting is transparent.