Geoff Ralston
President and Partner @ Y Combinator
San Francisco, United States
Geoff Ralston is a seed investor at Y Combinator in San Francisco focused on Software and Education. Geoff Ralston is the President, CEO, and Partner of Y Combinator. He previously worked at Imagine K12 as a Founder. Geoff Ralston attended INSEAD.
- Total investments:
- 50
- Last investment:
- Lead investor:
- 2%
Last updated:
For AI agents: llms.txt
Industries Geoff Ralston invests in
Stages Geoff Ralston invests in
Countries Geoff Ralston invests in
Round sizes
Contacts
| Type | Contact | Validation |
|---|---|---|
| Work email | ||
| Personal email | ||
| Work phone | ||
| Personal phone | ||
| Socials |
Round size
- Seed
- $1.1M–$4M
- Pre-Seed
- $125k–$4.2M
- Series A
- $3.2M–$12M
Investment Focus
Industry
- Software 12 (24%)
- Education 7 (14%)
- Artificial Intelligence 7 (14%)
- SaaS 4 (8%)
- Music 4 (8%)
Stage
- Seed 29 (58%)
- Series A 7 (14%)
- Pre-Seed 4 (8%)
- Angel 3 (6%)
- Funding Round 3 (6%)
Country
- United States 38 (76%)
- India 1 (2%)
- Senegal 1 (2%)
- South Korea 1 (2%)
Investments
| Company | Description | Round | Links |
|---|---|---|---|
| Asymmetric Security is an AI-native cybersecurity startup specializing in digital forensics and incident response. It combines elite forensic experts with proprietary AI to accelerate investigations, especially Business Email Compromise (BEC) attacks, at less than half the cost of competitors while shrinking timelines from days to hours. | $4.2M / Pre-Seed / Jan 23, 2026 | ||
| Actionable local reporting and civic intelligence at scale with journalist-in-the-loop AI. | $225K / Pre-Seed / Jul 17, 2025 | ||
| Every wildfire starts small. Rain contains wildfires within 10 minutes of ignition with autonomous drones. | $9.7M / Seed / Sep 21, 2023 | ||
| Turing College is an online tech school for AI & Data skills. Turing College delivers 100% government-sponsored programs in Lithuania, Germany, and the United Kingdom. | $125K / Pre-Seed / Feb 28, 2021 | ||
| Aesthetic's mission is to make the world more well designed by giving every business creative superpowers. To do this, we're automating all the production design work needed by companies, starting with social media graphics. Social media is an important marketing channel for businesses, but creating quality content is hard. Our productcreates the social marketing posts your brand needs without doing any design work. | $3.1M / Seed / Apr 28, 2020 | ||
| Elpha is where women in tech to talk candidly online. Join Elpha to find support, connect personally and professionally with other women in the industry, make friends, build your network and search for jobs. Membership is free! | $1.1M / Seed / Nov 06, 2019 | ||
| Next Tech makes it easy to run any program code or Linux-based software in the cloud, even from untrusted sources. Their browser-based integrated development environment (IDE), students and developers can build software without having to download anything.We strive to offer an IDE that perfectly walks the line between being a cumbersome developertool and a textbox that runs code. We believe that as the number of developers increases, the accessibility of the tools they use must increase at an equal rate to ensure that all are empowered to build what's next in tech. | $1.1M / Seed / Aug 01, 2018 | ||
| At Shield, we’re ensuring that antibiotic resistance doesn’t become more deadly than cancer.In 2050 more people will be dying of antibiotic resistant pathogens than cancer. Infections that were once treatable with a simple oral antibiotics are now requiring complex, painful treatments and resulting in serious health complications for patients.Gonorrhea is one such infection, having become resistant to over 10 different antibiotics, they have only one treatment that is still effective and resistance to this has already begun to emerge. With 820,000 new infections every year in the US, antibiotic resistance will spread quickly, which is why the CDC has resistant gonorrhea at an urgent threat level, the highest level available.Shield's novel genomic testing platform enables STI clinics to identify the antibiotic resistant strains of gonorrhea and other pathogens that their patients have, so they can select the correct antibiotics and halt the spread of antibiotic resistance. | $8M / Series A / May 23, 2018 | ||
| Oolu is the fastest growing off-grid solar company West Africa. Our Vision is to be the leading energy and financial service provider to millions of customers in the developing world.Our model, developed with local communities, allows us to reach off-grid households in rural villages offering them modern energy access. With a monthly paymentmodel reducing barriers to access, as well as maintenance, parts and battery replacements included in our service, we save our clients money and assure them a continuous, dependable source of energy. In Wolof, a national language of Senegal, Oolu means ‘trust’. By building trust with the communities in which we work, we can grow together. | $3.2M / Series A / Oct 09, 2017 | ||
| Dost builds software, audio content, and toolkits that make it easy, fun and addictive for parents of any literacy level to boost their child’s early development. | Seed / Mar 21, 2017 | ||
| See all 50 investments → | |||
Co-Investors
About Y Combinator
Y Combinator is a startup accelerator that provides funding and mentorship to early-stage companies. It offers a program where startups receive guidance from experienced entrepreneurs and investors. The organization helps founders in their business models and develop their products. Y Combinator serves industries such as technology, healthcare, andfinance.
Y Combinator Contacts
| Name | Phone | Socials | |
|---|---|---|---|
Boris Jabes
Visiting Partner
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Luther Lowe
Head of Public Policy
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Max Kolysh
Visiting Partner
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Brad Flora
Group Partner
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Calvin French-Owen
Visiting Group Partner
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FAQ
What does Geoff Ralston invest in?
Geoff Ralston invests primarily in Software, Education and Artificial Intelligence startups, most often at Seed and Series A stage. Most of the 50 investments tracked by Shizune back companies in United States. The Investment Focus section breaks down every industry, stage and country in the portfolio.
What is Geoff Ralston's check size?
Geoff Ralston typically joins rounds of $1.1M–$4M at Seed, $125k–$4.2M at Pre-Seed and $3.2M–$12M at Series A. These ranges are 10th–90th percentile round sizes calculated from confirmed public funding rounds, so they are a realistic guide to the rounds Geoff Ralston participates in.
How do I contact Geoff Ralston?
Public channels for Geoff Ralston include LinkedIn, X (Twitter) and Facebook. For a verified work email and phone number, create a free Shizune account — contact data is searched across 20+ sources and validated before delivery, so your outreach lands in the right inbox.
When did Geoff Ralston last invest?
The most recent investment recorded for Geoff Ralston closed in Jan 2026. Shizune tracks 50 investments in total for this profile, including round sizes, stages and portfolio companies, all sourced from confirmed public funding rounds and refreshed monthly.
Is Shizune's investor data accurate?
Yes — every stat on this profile is calculated from confirmed public funding rounds monitored across hundreds of sources since 2020. This profile was last refreshed in Sep 2026 and is updated monthly. Spotted something off? Use the “Suggest an edit” link near the top of the page.
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