# Series A/B venture capital rounds > The first two rounds of US-origin institutional venture capital, now the global standard for startup financing, channeling billions annually from VC firms into early-growth companies worldwide. **Meta:** type: reference · date: 2026-07-03 · heads: · 3 takes · 3 lenses · 1 regions ## What it is Series A and Series B are the first two rounds of institutional venture capital, named after the class of preferred stock issued to investors in each round. The lettered convention traces to US corporate law: each round of preferred stock is sequentially lettered, so the first institutional round is Series A, the second Series B, and so on. A Series A round is typically the first time a startup accepts capital from an institutional VC firm, having already demonstrated initial product-market fit through angel or seed funding. Series B follows to finance scaling operations once the commercial model is validated. The structure originated in the United States in the 1970s and became the global standard for private startup financing from San Francisco to Lagos. Leading institutional participants at the Series A/B stage include Andreessen Horowitz, Sequoia Capital, Accel, Lightspeed Venture Partners, and sector-specialist funds; their counterparts in Europe, India and Southeast Asia follow broadly analogous structures. ## History The structured, alphabetically-labelled preferred-stock round emerged from US West Coast VC practice in the late 1970s, codified around large limited-partnerships including Sequoia Capital (founded 1972) and Kleiner Perkins (founded 1972). Median US Series A sizes were below US$5m through much of the 2000s, rose to US$7-10m during the 2010s expansion, and crossed US$15m during the 2020-2021 zero-rate environment. The US Federal Reserve's rate increases from 2022 temporarily compressed deal volumes. By 2024 the market had bifurcated: AI-linked companies attracted outsized valuations while non-AI startups faced tighter terms and longer timelines to close. The Series A/B structure spread to European markets in the 1990s, to India and Southeast Asia in the 2000s, and to Africa and Latin America in the 2010s, typically co-invested by regional funds alongside US-domiciled lead investors. ## Current state As of Q1 2026, the United States remains the world's largest Series A/B market by volume and capital. The PitchBook-NVCA Venture Monitor for Q1 2026 recorded a US median Series A deal size of US$19.6m against a mean of US$39.6m, a bimodal distribution driven by AI companies raising at multiples of the historical median. More than half of early-stage deals in Q1 2026 exceeded US$10m, the highest share in a decade. AI accounted for over half of megadeal flow, compressing timelines from incorporation to Series A, with some companies securing institutional rounds within 12 months of founding. [Generalist AI's US$400m Series A at a US$2bn valuation in June 2026](/zh/n/generalist-ai-series-a-2026) is the largest single Series A in US robotics AI this year, a round that stretches the label well beyond its historical size range. [Biotech VC](/zh/n/biotech-vc-dossier) runs a parallel Series A/B market with overlapping investors but different timelines tied to regulatory milestones rather than revenue traction. [African startup markets](/zh/n/africa-startup-funding-h1-2026) are adopting the Series A/B structure at smaller sizes, typically US$5-20m at Series A. ## Relationships Series A/B rounds sit between seed capital and later-stage growth equity in the startup capital stack. Seed investors (US$500k-US$5m) include angel networks, accelerators such as Y Combinator, and pre-seed micro-VCs. Series A/B investors are primarily closed-end VC funds with 10-to-12-year lives whose returns depend on exits via IPO or acquisition. [Andreessen Horowitz (a16z)](/zh/n/a16z-dossier) is among the most active Series A/B investors by deal count across software, AI, crypto and bio verticals as of mid-2026, having raised US$7.2bn in its most recent flagship fund. The [foundation-model startup sector](/zh/n/foundation-model-startups-dossier) has stretched the Series A label furthest, with rounds above US$100m now classified as Series A based on company age rather than size, because these companies raise institutional capital before generating meaningful revenue. ## What to watch - Whether the AI-driven gap between median (US$19.6m) and mean (US$39.6m) US Series A sizes widens or normalizes through the rest of 2026. - How US Federal Reserve rate decisions affect Series B valuations, which are more exposed to discounted-cash-flow-sensitive late-stage crossover investors. - The pace of robotics and embodied-AI Series A deals following [Generalist AI's record round](/zh/n/generalist-ai-series-a-2026), as hardware-plus-model startups attract larger institutional commitments. - Whether [African and Southeast Asian markets](/zh/n/africa-startup-funding-h1-2026) develop enough domestic capital depth to lead Series A rounds without requiring a US co-lead. - IPO window conditions on the US Nasdaq, which govern fund recycling and risk appetite for new early-stage commitments. ## Regional takes (batched by bias / lens) ### institutional VC data - **PitchBook-NVCA Venture Monitor** (United States, en) — Quarterly authoritative report from the US National Venture Capital Association and PitchBook tracking deal volume, stage mix and capital flows across US venture; Q1 2026 edition recorded a median Series A of US$19.6m against a mean of US$39.6m. Source: https://nvca.org/pitchbook-nvca-venture-monitor/ ### quarterly VC statistics - **Q1 2026 PitchBook-NVCA Venture Monitor (PDF)** (United States, en) — Full Q1 2026 data pack: US$267.2bn total deal value, median early-stage deal above US$10m for the first time in a decade, AI accounting for over half of megadeal flow, with five deals representing 73% of total capital deployed. Source: https://nvca.org/wp-content/uploads/2026/04/Q1-2026-PitchBook-NVCA-Venture-Monitor.pdf ### practitioner explainer - **Silicon Valley Bank: Stages of Venture Capital** (United States, en) — SVB's practitioner guide to the VC funding ladder from seed through growth equity, covering what investors look for at Series A (product-market fit) and Series B (commercial viability and scale readiness). Source: https://www.svb.com/startup-insights/vc-relations/stages-of-venture-capital/ ## Across the graph - Related: [[generalist-ai-series-a-2026]], [[a16z-dossier]], [[biotech-vc-dossier]], [[africa-startup-funding-h1-2026]], [[foundation-model-startups-dossier]] - Entities: Series a, Venture Capital, Region:silicon Valley, Seed Funding, Ipo Markets --- Canonical: https://rbtfl.xyz/zh/n/series-a-dossier