Castle Island Ventures is a Cambridge, Massachusetts–based venture capital firm focused exclusively on public blockchain networks and the companies built on them. Founded in 2018 by Nic Carter and Matt Walsh, the firm takes a thesis-driven approach: it backs businesses that depend on open, permissionless blockchains rather than private distributed ledger projects. This conviction has kept its portfolio concentrated in Bitcoin infrastructure, stablecoins, custody, compliance tools, and decentralized finance.
The firm has raised at least two funds since inception. Fund I closed at approximately $30 million in 2018, and Fund II followed in 2020 at a similar size. A third vehicle was reportedly in formation in the 2022–2023 period, though Castle Island has not publicly disclosed final figures for later funds. Total AUM as of mid-2026 is not publicly confirmed. The firm typically writes early-stage checks and leads seed or Series A rounds, consistent with its lead investment count of 26 across a disclosed portfolio of 11 active companies.
Castle Island focuses primarily on the United States and Western Europe, with a stated preference for companies building regulated or regulation-ready products. This has shaped a portfolio skewed toward infrastructure that institutional clients can use – custody, analytics, and payment rails rather than speculative tokens.
Notable investments
- Anchorage Digital – institutional crypto custody platform; became the first federally chartered crypto bank in the United States in January 2021 under the OCC.
- Compound Finance – decentralized lending protocol on Ethereum; one of the earliest DeFi blue chips and a foundational piece of the open finance stack.
- TRM Labs – blockchain intelligence and transaction monitoring for financial institutions and government agencies.
- River Financial – Bitcoin-only brokerage and Lightning Network node operator serving retail and institutional clients.
- Bitwise Asset Management – crypto index funds and ETF products; became a major player in the Bitcoin spot ETF approval cycle of 2024.
- Silvergate Bank – early and significant investment in the crypto-friendly bank that operated the Silvergate Exchange Network (SEN). Silvergate entered voluntary liquidation in March 2023, representing a notable loss in the portfolio.
Team
Nic Carter is a general partner and one of the most recognised researchers in the Bitcoin space. Before co-founding Castle Island, he was a crypto analyst at Fidelity Investments and co-founded Coin Metrics, an on-chain data company. He writes and speaks extensively on Bitcoin, monetary policy, and regulatory issues. His commentary on proof-of-work, stablecoins, and crypto banking has been cited in academic and policy contexts.
Matt Walsh is a general partner who handles much of the operational and deal side of the firm. Prior to Castle Island, Walsh worked in traditional finance and early-stage venture. Public information about his pre-2018 background is limited compared to Carter's public profile, but he is credited with much of the portfolio construction work on later-stage follow-on decisions.
Recent activity
Through 2024 and into 2025, Castle Island was active in the stablecoin infrastructure space as regulatory clarity improved in the United States. The firm publicly supported the legislative effort around the GENIUS Act and similar stablecoin frameworks. Carter was vocal about the importance of bank-issued and regulated stablecoins versus offshore alternatives. The firm's earlier Anchorage investment benefited from the OCC charter remaining intact through successive administrations.
The Silvergate failure in early 2023 tested the portfolio but did not derail the firm's fundraising trajectory. Castle Island has generally avoided investments in exchanges, which spared it from direct exposure to the FTX collapse in late 2022. Its focus on compliance and custody infrastructure proved defensible during the 2022–2023 sector shakeout.
Looking ahead, Castle Island is positioned around two durable themes: Bitcoin as a reserve and payment asset, and regulated stablecoin infrastructure. Both themes have gained institutional momentum since 2024. The firm's relatively small fund sizes mean it cannot lead mega-rounds, but its early positioning in companies like Anchorage and Bitwise gave it credibility with limited partners who prioritise quality over deployment pace. With a retail ROI of 0.79 across disclosed positions, returns have been modest relative to headline crypto gains – a reflection of the firm's conservative, infrastructure-first bets rather than high-beta token exposure.
